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Journal of Ecology 2018106655ndash670 wileyonlinelibrarycomjournaljec emsp|emsp655copy 2017 The Authors Journal of Ecology copy 2017 British Ecological Society
Received23May2017emsp |emsp Accepted17October2017DOI1011111365-274512901
R E S E A R C H A R T I C L E
Direct and indirect controls on organic matter decomposition in four coastal wetland communities along a landscape salinity gradient
Camille L Stagg1 emsp|emspMelissa M Baustian2 emsp|emspCarey L Perry34emsp|emspTim J B Carruthers2emsp|emsp Courtney T Hall1
1USGeologicalSurveyWetlandandAquaticResearchCenterLafayetteLAUSA2TheWaterInstituteoftheGulfBatonRougeLAUSA3CoalitiontoRestoreCoastalLouisianaBatonRougeLAUSA4LouisianaDepartmentofWildlifeandFisheriesBatonRougeLAUSA
CorrespondenceCamilleLStaggEmailstaggcusgsgov
Funding informationUSGeologicalSurveyClimateResearchandDevelopmentProgramUSGeologicalSurveyEcosystemsProgramUSGeologicalSurveyLandCarbonProgramScienceandEngineeringProgramofTheWaterInstituteoftheGulfLouisianaCoastalProtectionandRestorationAuthority(CPRA)BatonRougeAreaFoundation(BRAF)RestoretheMississippiRiverDeltaCampaignviaCoalitiontoRestoreCoastalLouisiana(CRCL)
HandlingEditorAmyZanne
Abstract1 CoastalwetlandsstoremorecarbonthanmostecosystemsgloballyAssealevelriseschangesinfloodingandsalinitywillpotentiallyimpactecologicalfunctionssuch as organicmatter decomposition that influence carbon storageHoweverlittle isknownabout themechanisms thatcontrolorganicmatter loss incoastalwetlandsatthelandscapescaleAssealevelriseshowwilltheshiftfromfreshtosalt-tolerant plant communities impact organicmatter decompositionDo long-termplant-mediatedeffectsofsea-levelrisedifferfromdirecteffectsofelevatedsalinityandflooding
2 Weidentifiedinternalandexternalfactorsthatregulatedindirectanddirectpath-waysofsea-levelriseimpactsrespectivelyalongalandscape-scalesalinitygradi-entthatincorporatedchangesinwetlandtype(fresholigohalinemesohalineandpolyhalinemarshes)Wefoundthatindirectanddirectimpactsofsea-levelrisehadopposingeffectsonorganicmatterdecomposition
3 Salinityhadanindirecteffectonlitterdecompositionthatwasmediatedthroughlitter qualityDespite significant variation in environmental conditions along thelandscapegradientthebestpredictorsofabove-andbelow-groundlitterdecom-positionwereinternaldrivers initial litternitrogencontentandinitial litter lignincontentrespectivelyLitterdecayconstantsweregreatestintheoligohalinemarshanddeclinedwithincreasingsalinityandthefractionof litterremaining(asymp-tote)wasgreatestinthemesohalinemarshIncontrastdirecteffectsofsalinityandfloodingwerepositiveExternaldriverssalinityandfloodingstimulatedcellulyticactivitywhichwashighestinthepolyhalinemarsh
4 SynthesisOurresultsindicatethatassealevelrisesinitialdirecteffectsofsalinitywillstimulatedecayoflabilecarbonbutovertimeasplantcommunitiesshiftfromfresh topolyhalinemarsh litterdecaywill decline yieldinggreaterpotential forlong-termcarbonstorageThesefindingshighlighttheimportanceofquantifyingcarbon loss atmultiple temporal scales notonly in coastalwetlandsbut also inother ecosystems where plant-mediated responses to climate change will have significantimpactsoncarboncycling
656emsp |emsp emspenspJournal of Ecology STAGG eT Al
1emsp |emspINTRODUCTION
Climatechange-inducedshiftsinvegetationcommunitycompositionwillhaveimportantimplicationsforecologicalfunction(Woltersetal2000) and ultimately carbon cycling (Jobbagy amp Jackson 2000) Interrestrial ecosystems shifts in vegetation community compositionhavebeenobservedinresponsetoelevatedatmosphericcarbondi-oxide (Leadley Niklaus Stocker amp Korner 1999 Owensby CoyneHamAuenampKnapp1993)elevatedairsoilandwatertemperatures(AlwardDetling ampMilchunas 1999Harteamp Shaw 1995) alteredprecipitation patterns (Sternberg Brown Masters amp Clarke 1999)andtheirinteractions(Kardoletal2010)Coastalmarshessituatedbetweenterrestrialandmarineecosystemsareexposednotonlytotheseclimaticdrivers(Oslandetal2016OslandEnwrightampStagg2014)butalsotoanthropogenicpressuresalongthelandwardbound-aryandrisingsealevelsalongtheseawardboundary(Dayetal2008SmallampNicholls2003)
Sea-level rise can force shifts in wetland vegetation commu-nity composition by altering flooding and salinity regimes (BurdickampMendelssohn 1987 DeLaune Patrick amp Pezeshki 1987 HesterMendelssohn amp McKee 2001 Krauss etal 2009 McKee ampMendelssohn1989)Assalinityincreaseswithsea-levelrisemarshhab-itatswillconverttocommunitiesdominatedbymoresalt-tolerantplantspecies(SharpeampBaldwin2012WarrenampNiering1993)Moreoveranthropogenic restrictions toupslopemigration (EnwrightGriffithampOsland2016)inconjunctionwithsea-levelrisemayresultintheex-pansionof saltmarshesat theexpenseofotherwetland typesyield-ing anoverall shift tomore saline conditions (VisserDuke-SylvesterCarterampBroussard 2013)Changes inwetlandecosystem structuremayeventuallyreflectalteredecological functionandecosystemser-vicesIntidalfreshwaterforestedwetlandsimpactedbysea-levelrisethetransitiontoherbaceousoligohalinemarshresultedingreaternitro-genandphosphorusmineralization fluxesandturnover (NoeKraussLockabyConnerampHupp2013)Similarlythetransitionofherbaceoussaltmarshtomangroveforestsignificantlyalteredecosystemfunctionwith greater carbon sequestration rates and lignin storage rates in mangrovescomparedtosaltmarshes(Bianchietal2013)
Coastalwetlands provide numerous ecosystem services (Barbieretal2011)includingsignificantcarbonstorageinlivingandnon-livingbiomassandinfloodedsoils(McCleodetal2011)Furthermoreunliketerrestrialsoilsthatmaybecomecarbon-saturatedovertime(StewartPaustianConantPlanteampSix2007)coastalwetlandscontinuallyac-cretemineralsedimentsandorganicmattertokeeppacewithsea-levelrise(Reed1995)thusthepotentialforcarbonstorageinwetlandsoilsincreasesovertime(ChmuraAnisfeldCahoonampLynch2003)
Carbon storage in wetlands is the net result of organic matterproduction and organic matter loss for example decomposition
Decompositionoforganicmatterisinfluencedbyinternalandexternaldrivers(GodshalkampWetzel1978)Whenconsideringtheeffectofanultimatedriversuchassea-levelriseonorganicmatterdecomposi-tioninternalandexternaldriverswillhaveindirectanddirectimpactsrespectivelyonthefateoforganicmatter Internaldriversarechar-acteristicsof theorganicmatter itself and includequalitiesofplantmorphologyandchemicalcompositionof theplantmaterial (McKeeampSeneca1982MelilloNaimanAberampLinkins1984)Incontrastexternaldriversofdecompositionarecharacteristicsoftheenviron-mentandincludesoilmicrobeanddetritivorecommunitycomposition(MorriseyBerrierNeubauerampFranklin2014Valielaetal1985)andabiotic conditions suchas soil temperature flooddurationand fre-quencyandsalinity(ReddyampPatrick1975WestonDixonampJoye2006)Therefore sea-level rise has the potential to impact organicmatterdecompositionindirectlybyforcingshiftsinplantcommunitycompositionandlitterquality(internalcontrols)anddirectlythroughalteringsalinityandflooding(externalcontrols)(StaggSchoolmasterKrauss Cormier amp Conner 2017) Furthermore these indirect anddirect impacts are resolved at different spatial and temporal scales(Herbertetal2015NeubauerFranklinampBerrier2013)thereforeitiscriticalthatwequantifybothinternalandexternalcontrolsonor-ganicmatterdecompositionifwehopetoaccuratelypredictthefateoforganicmatterinafuturewithsea-levelrise
Although there has been much recent progress in elucidatingfine-scale mechanisms of soil respiration in response to elevatedsalinity (Chambers Osborne amp Reddy 2013 Chambers Reddy ampOsborne 2011 Neubauer 2013 Neubauer etal 2013 WestonVileNeubauerampVelinsky2011Westonetal2006)westilllackacomprehensiveunderstandingofthemechanismsthatcontrolorganicmatterdecompositionincoastalwetlandsatthelandscapescale(butseeJanouseketal2017WestonNeubauerVelinskyampVile2014)To address thiswemeasured decomposition of in situ litter and astandardizedcarbonsourceacrossalandscape-scalesalinitygradientthatincorporatedchangesinvegetationcommunitytoaddressthefol-lowingresearchquestions(1)Whatdriversinfluenceorganicmatter decompositionalongalandscapesalinitygradientincoastalmarshes(2)Howdo long-term indirect impactsof sea-level risediffer fromshort-termdirectimpactsofsea-levelriseonorganicmatterdecom-positionand(3)Whataretheimplicationsforlong-termcarbonstor-ageinestuarinecoastalwetlandsimpactedbysea-levelrise
2emsp |emspMATERIALS AND METHODS
21emsp|emspStudy sites
Above- and below-ground decomposition was measured in es-tuaries along a landscape-scale (c 65km) salinity gradient that
K E Y W O R D S
carboncellulosedecaycoastalwetlandslandscapelitterdecompositionplantcommunityplant-climateinteractionssea-levelrise
emspensp emsp | emsp657Journal of EcologySTAGG eT Al
incorporatedfresh(0ndash05ppt)oligohaline(05ndash5ppt)mesohaline(5ndash18 ppt) and polyhaline (gt18 ppt) coastal marshes as definedby Cowardin Carter Golet and LaRoe (1979) (Figure1) Due tohightemporalvariationinsalinitywetlandcommunitytypesweredefined not only bymeasured salinity but also by dominant veg-etation species known to be associatedwith specific salinity andhydrologicalregimes(VisserSasserChabreckampLinscombe2002)FreshsitesweredominatedbyPanicum hemitomon and Typha lati-folia oligohaline siteswere dominated by Sagittaria lancifolia and Schoenoplectus americanus mesohaline sites were dominated bySpartina patens and S americanusandpolyhalinesitesweredomi-natedbySpartina alterniflora and Juncus roemerianusWithineachofthefourwetlandtypessixreplicatesiteswereestablishedacrosstwohydrologicbasinsTerrebonneandBaratariaBasinsforatotalof24sites(Figure1Baustianetal2017Staggetal2017)
22emsp|emspResponse variables
221emsp|emspLitter decomposition
Rates of above- and below-ground organic matter decompositionweremeasuredusingthelitterbagtechnique(HackneyampdelaCruz1980) which integrates short- and long-term decomposition pro-cesses associatedwith labile and refractory organicmatter (Valielaetal1985)Litterbagscontainingsite-specificabove-groundbiomassand litterbags containing site-specific below-groundbiomass or lit-terwere installed inthreereplicateplots ineachsiteLivebiomassof each site-specific dominant specieswas collected from a subsetofsiteswithineachwetlandtypeandhydrologicbasin(subsetn=8)in July2014Above-groundbiomassofeachdominantspecieswascollectedfromamonospecificstandclippedat thesoilsurfaceandsortedintoliveanddeadpoolsuponreturningtothelaboratoryTo
collectbelow-groundbiomass in largequantities 20-cmwidetimes30-cmdeepsodswereharvestedfrommonospecificstandsrepresentingeachdominantspeciesThesodsweretransportedbacktothelabora-torywherethebelow-groundbiomasswasrinsedovera1-mmsieveto remove soil particles The remaining macro-organic matter wasseparated into live and dead components Live roots and rhizomesweredistinguishedfromdeadrootsandrhizomesbycolourturgidityandstructuralintegrity(SchubauerampHopkinson1984)Above-andbelow-groundlivebiomasswasallowedtoair-drytoaconstantmassforatleast1weekbeforeplacementinlitterbagsLiveair-driedlitterwas used in place of senesced litter to captureweight loss associ-atedwithinitialdecayprocessessuchasleachingthatwouldhaveal-readyoccurredinsenescedmaterialcollectedfromthefield(McKeeampSeneca1982)Above-groundlitterbagswerepreparedbyfillingmeshbags(20cmlongtimes20cmwidetimes15mmopening)withliveair-driedleafandstemmaterial(20gbag)Below-groundlitterbagswerepre-paredbyfillingmeshbags(8cmlongtimes20cmwidetimes10mmopening)with live air-dried roots and rhizomes (5gbag) Generally above-groundlitterbagshavealargermeshopeningthanbelow-groundlit-terbags(HalupaampHowes1995HemmingaKokampdeMunck1988)toallowforthepassageofsmallandyounginvertebrates(McKeeampSeneca1982)Asubsampleofthe initialair-driedmaterial foreachspecieswasweighedoven-driedat60degCandreweighedtocalculateamoisturecorrectionfactorwhichwasappliedtothestartingmass(w0)ofair-driedlitterusedinsubsequentcalculations
Above- and below-ground litterbag transects were establishedperpendicular to thewater body and included three replicate plotslocated 10 25 and 40m from the shorelineAbove-ground litterb-agsweresecuredonthesoilsurfacewithlandscapepinsandbelow-ground litterbags were inserted into the soil to a depth of 10cmFourlitterbagswereinstalledineachreplicateplot inOctober2014(n=288 above-ground litterbags n=288 below-ground litterbags)
F IGURE 1emspDecompositionstudysiteslocatedalongalandscape-scalesalinitygradientspanningfourwetlandtypesincoastalLouisianaUSA
658emsp |emsp emspenspJournal of Ecology STAGG eT Al
andindividual litterbagswereretrievedfromeachplotatfour inter-vals(136and12monthsafterinstallation)tofollowamodelofex-ponential decayAfter retrieval the above- and below-ground litterbagsweregentlyrinsedwithdeionizedwaterovera1-mmsieveandremaininglitterwasoven-driedforatleast48hrtoaconstantmassat60degC(HalupaampHowes1995)Thelitterwasthenweighedandre-tainedforfurtherchemicalanalysesPercentmassremaining(MR)wascalculatedusingthefollowingequation
where w0isdryweightattimezeroandwtisdryweightattimet(daysafterinstallation)
The proportion of mass remaining over timewas used to esti-mate two parameters that describe the decomposition process (1)thedecayrateorexponentialdecayconstantand(2)theasymptoteornon-decomposable fractionTheexponentialdecayconstantwas derivedusingasinglenegativeexponentialdecaymodel
where X ispercentmassremainingaftertimet (daysafter installa-tion)andminuskistheinstantaneousdecayconstant(perday)(WeiderampLang1982)Additionallyweusedanasymptoticmodel toestimatethenon-decomposablefractionorasymptote
where Caistheasymptoteorfractionofmaterialremaining(WeiderampLang1982)Becausethesingleexponentialdecaymodelprovidedabetterfitfordecayconstantestimatesweonlyusedtheasymptoticmodeltoestimateasymptotesnotdecayconstants
222emsp|emspCellulose decay
Inadditiontolitterdecompositionwealsomeasuredcellulyticactivityusingthecottonstriptechniquewhichprovidesameasureofshort-termlossoflabilecarbon(Maltby1988)Cottonstripsaremadefromartistcanvaswhichiscomprisedof98holocelluloseandbyusingastandardizedcarbonsourcewewereabletoisolateexternalfactorsthat influencemicrobial activity (Mendelssohn etal 1999 SlocumRobertsampMendelssohn2009)
Cottonstripswereinstalledinthreereplicateplotsalongatran-sect parallel to the litterbag transects Below-ground cotton strips(10-cmwidetimes30-cmlong)wereinsertedverticallyintothesoiltoadepthof25cmThecottonstripsweredeployedfourtimesseason-allyandretrievedafter12ndash14daysinthesoildependingonthewatersurfacetemperature(Slocumetal2009)Above-groundcottonstrips(20cmtimes20cm)weredeployedinOctober2015securedtothesoilsurfaceusinglandscapepinsandretrieved14dayslaterThreecot-tonstrips(twoteststripsandonereferencestrip)wereplacedineachreplicatedplotReferencestripsusedtoquantifythetensilestrengthofnon-decomposedmaterialwerehandledexactlythesameastheteststripsbutretrievedimmediatelyafterdeployment
After retrieval cotton strips were rinsed gently with deionizedwatertoremoveallsoilandextraneousmaterialandthecottonstripswereallowedtoair-dryforatleast48hrCottonstripswerecutinto
2-cm substrips along the vertical profile and decomposition of the2-cm substripswasmeasured as tensile strength lost compared tothe reference substrip using a Dillon Quantroltrade Snapshot TensionCompressionMotorizedTestStandtensometerconnectedtoaDillonQuantroltrade Advanced Force Gauge (Slocum etal 2009) Cellulosedecay ratewascalculatedasper cent cellulose tensile strength lostperday(CTSLperday)
whereT is the force (N) requiredto tear thetestsubstripsR is theforce(N)requiredtotearthereferencesubstripsandtistime(days)inthemarsh
23emsp|emspPredictive variables
231emsp|emspExternal drivers
All study sites were located within the 1-km2 boundary of aCoastwide Reference Monitoring Systems station (httplacoastgovcrms2homeaspx) where surface water salinity and surfacewater elevation are measured hourly Marsh surface elevation of15plotswithineachsite (n=360)weresurveyedusingRealTimeKinematicmethodology(GaoAbdel-SalamChenampWojciechowski2005)withaTrimbleR10GNSSSystem(TrimbleNavigationLimitedUSAChenetal2011)andrectifiedtotheNorthAmericanVerticalDatumof1988(NAVD88)usingTrimbleBusinessCenter25soft-ware for data post-processing (Trimble Navigation Limited USA)We usedmarsh elevation data in conjunctionwith surfacewaterelevationdatatocalculateflooddepthanddurationforeachof15plotsineachsite
Discrete soil and porewater sampleswere taken to measure asuiteofenvironmentalparameters inDecember2014Ateachsitetwosoilcores(10-cmdiametertimes30-cmlength)werecollectedneareachofthethreereplicatedplotsalongthebelow-ground litterbagtransect(n=72)Aftercollectionthesoilcoresweresectionedintotwoincrements(0ndash15cmand16ndash30cm)andimmediatelyplacedonice in the fieldand transportedback to the laboratorywhere theywerehomogenizedThefirstcorewasusedforanalysisofsoilbulkdensity (Blake 1965) moisture (Blake 1965) organic mat-ter (OliverLotterampLemcke2001)andelectricalconductivity (ECRhodes1996)
ThesecondsoilcorewasusedtomeasuresoilpH(Thomas1996)soiltotalCNandPsoilextractablenutrients(PO4-PandNH4-N)andotherelementsofinterest(CaCuFeKMgNaNiP)Thehomog-enizedsoilwasdriedtoaconstantweightat60degCgroundinaWileyMill(Model420mesh850μm)andseparatedintoseveralscintil-lationvials formultipleanalysesSoil totalNandtotalCweremea-suredusingaCostechreg4010ElementalCombustionanalyzer(Nelsonamp Sommers 1982 EPAMethod 440) Extractionswere performedforthefollowinganalysessoiltotalP(HClAspilaAgemianampChau1976)PO4-P(Bray-2OlsenampSommers1982)NH4-N(KClKeeneyampNelson1982)andotherparametersofinterest(H2NO3AmericanPublic Health Association 2005a) Soil total P PO4-P samples and
MR= (wt∕w0)times100
X=eminuskt
X=Ca+ (1minusCa)eminuskat
CTSL per day= [1minus (T∕R)times100]∕t
emspensp emsp | emsp659Journal of EcologySTAGG eT Al
NH4-N were measured on a segmented flow AutoAnalyzer (FlowSolution IVAutoAnalyzer O-I Analytical USA EPAMethod 3655EPAMethod 3501)The remaining extractswere analysedwith aninductivelycoupledargonplasmaopticalemissionspectrometer(ICP-OES)(Varian-MPXAgilantUSAAmericanPublicHealthAssociation2005b)
Simultaneously four separate aliquots of porewaterwere col-lectedfromadepthof10cmusingthesipper-tubemethod(VasilasampVasilas2013)Onealiquotofwaterwasused tomeasurepore-water pH (EPA Method 1501) and salinity (EPA Method 1201)The second porewater sample was used to measure porewatertotalNand totalP followingpersulfateoxidation (DrsquoEliaSteudlerampNathaniel1977EbinaTsutsuiampShirai1983)onasegmentedflowAutoAnalyzer (Flow Solution IVAutoAnalyzerO-IAnalyticalUSA)Thethirdaliquotwasfilteredthrougha045-μmfiltertomea-sureNH4-NandPO4-PusingasegmentedflowAutoAnalyzer(FlowSolution IVAutoAnalyzerO-IAnalytical USA EPAMethod3655EPAMethod3501)Thefourthaliquotwasfirstfiltered(45μm)andthenacidifiedtopHlt2tomeasureotherelementsofinterestusingan inductively coupled argon plasma optical emission spectrome-ter (ICP-OES) (Varian-MPX Agilant USA American Public HealthAssociation2005b)
232emsp|emspInternal drivers
Above- and below-ground biomass from each wetland type alongthesalinitygradientwascollectedtocharacterizechemicalcomposi-tionofthelitterinJuly2013and2014InJuly2014subsamplesofinitialabove-andbelow-groundair-driedbiomasscollectedforeachrelevantdominantspecieswithineachwetlandtypewereanalysedfor lignin contentusing theacid-detergent fibreandacid-insolubleash techniques (Van Soest amp Wine 1968) Because insufficientinitial biomass remained for further analyses separate vegetationsamplespreviouslycollectedfromthestudysitesandanalysedfortotalCandtotalNinJuly2013servedasaproxyforthelitterusedin the litterbags In July 2013 above-ground biomasswas clippedat thesoil surface from025-m2quadrats separated into total liveandtotaldeadcomponentsandweighedafterdryingtoaconstantmassat60degC(Mendelssohn1979)Afterabove-groundbiomasswasremovedfromtheplotasharpened10-cmPVCcorerwasusedtocollectbelow-groundbiomass from thecentreof thequadratThecoresweretakentoamaximumdepthof30cmortheentirerootmatthicknessandwerewashedina1-mmsievetoremovesoilpar-ticlesLiverootsandrhizomeswereseparatedfromdeadrootsandrhizomes and the remainingmatrixof deadorganicmaterial baseduponbiomasscolourturgorandbuoyancy(SchubauerampHopkinson1984)Allmaterialwasdriedat60degCtoaconstantmassandweighedAbove-andbelow-groundvegetationsampleswerethengroundinaWileyMill (Model420mesh850μm)oven-driedat60degCandanalysed for totalCand totalNusingaCostechreg 4010ElementalCombustionanalyzer(NelsonampSommers1982EPAMethod440)Only values for live biomass samples were used in subsequent statisticalanalyses
24emsp|emspStatistical analysis
We used a nonlinear regression to estimate decay constants andasymptotes from single exponential decay models and asymptoticmodelsrespectivelyNonlinearregressionmodelsweredevelopedforeach plot in each site (above-groundn=72 below-groundn=72)Onlyestimates frommodels thatsuccessfullyconvergedwereusedinsubsequentstatisticaltestsWeusedamixed-modelANOVAwitharandomizedcompleteblockdesignwithsamplingtocomparevari-ation in response variables (decay constants asymptotes cellulosedecay rates) The fixed effect of wetland type was the treatmenteffect basins represented error associatedwith blocking and threesiteswithineachbasinbywetlandtypetreatmentcombinationrep-resentedsite-levelerrorResponsevariablesweremeasuredinthreeplots within each site which represented sampling error Principalcomponentanalysis(PCA)wasusedtoexplainvariationintheenvi-ronmentalparameterdatasetandananalysisofsimilarity(ANOSIM)wasperformedtodeterminewhethertheprincipalcomponents(PCs)variedsignificantlyamongthetreatmentgroups (wetlandtype)Wecalculated correlation coefficients tomeasure the linear associationbetweenredoxpotentialandPCfactorscoresFinallyweperformedmultiple linear regression analysis using the lm function to identifysignificantpredictorsofdecompositionForeach responsevariableweidentifiedafullmodelapriorithatincludedexplanatoryvariablesofknownimportanceandrelevanceThelitterdecompositionmodelspredictedabove-orbelow-groundlitterdecompositionrateasafunc-tionoflitterqualitysoilandporewaterphysico-chemistryandflood-ing The cellulose decaymodels predicted above- or below-groundcellulose decay rate as a function of soil and porewater physico-chemistryandfloodingWeusedprincipalcomponentfactorsasex-planatoryvariablestorepresentporewaterandsoilphysico-chemistryand flooding Because not all litter quality parameterswere signifi-cantlycorrelatedwithaprincipalcomponentweincludedlitterligninandnitrogencontentasexplanatoryvariablesinthemultipleregres-sionanalysesusing theobserveddata inplaceof the factorscoresThe following analyses were performed in SAS 93 software (SASInstitute Inc 2011) nonlinear regression (proc nlin) ANOVA (procmixed) and correlation analysis (proc corr) The following analyseswereperformedusingRsoftware(RDevelopmentCoreTeam2013)PCAANOSIMandmultiplelinearregression
3emsp |emspRESULTS
31emsp|emspResponse variables
311emsp|emspLitter decomposition
Inallwetlandtypesabove-andbelow-groundlittersignificantlyde-clinedwith time (Table1Figure2)Therewasa significant interac-tionbetweenabove-andbelow-grounddecayrateandwetlandtype(p=0004 df = 3 F=646) however regardless of wetland typeabove-ground litterdecomposed faster thanbelow-ground litter Inbothabove-andbelow-groundlitterpoolsthedecayratewasgreatest
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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AertsRampdeCaluweH(1997)Nutritionalandplant-mediatedcontrolson leaf litterdecompositionofCarex speciesEcology 78 244ndash260httpsdoiorg1018900012-9658(1997)078[0244NAPMCO]20 CO2
Alward R Detling J amp Milchunas D (1999) Grassland vegetationchangesandnocturnalglobalwarmingScience 283118ndash231httpsdoiorg101126science2835399229
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AmericanPublicHealthAssociation(2005b)3120metalsbyplasmaemis-sionspectroscopy(85)InADEatonampMAFranson(Eds)Standard methods for the examination of water and wastewater(21stedpp377ndash386)WashingtonDCAmericanPublicHealthAssociation
emspensp emsp | emsp667Journal of EcologySTAGG eT Al
AspilaKAgemianHampChauS(1976)Asemi-automatedmethodfordeterminationofinorganicorganicandtotalphosphateinsedimentsAnalyst 101187ndash197httpsdoiorg101039an9760100187
Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
BarbierEHackerSKennedyCKochEWStierACSillimanBR(2011)ThevalueofestuarineandcoastalecosystemservicesEcological Monographs 81169ndash193httpsdoiorg10189010-15101
BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
+ uptake inSpartina alterniflora Oecologia 85 375ndash380httpsdoiorg101007BF00320613
Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
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NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
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emspensp emsp | emsp669Journal of EcologySTAGG eT Al
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OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
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PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
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Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
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SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
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StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
656emsp |emsp emspenspJournal of Ecology STAGG eT Al
1emsp |emspINTRODUCTION
Climatechange-inducedshiftsinvegetationcommunitycompositionwillhaveimportantimplicationsforecologicalfunction(Woltersetal2000) and ultimately carbon cycling (Jobbagy amp Jackson 2000) Interrestrial ecosystems shifts in vegetation community compositionhavebeenobservedinresponsetoelevatedatmosphericcarbondi-oxide (Leadley Niklaus Stocker amp Korner 1999 Owensby CoyneHamAuenampKnapp1993)elevatedairsoilandwatertemperatures(AlwardDetling ampMilchunas 1999Harteamp Shaw 1995) alteredprecipitation patterns (Sternberg Brown Masters amp Clarke 1999)andtheirinteractions(Kardoletal2010)Coastalmarshessituatedbetweenterrestrialandmarineecosystemsareexposednotonlytotheseclimaticdrivers(Oslandetal2016OslandEnwrightampStagg2014)butalsotoanthropogenicpressuresalongthelandwardbound-aryandrisingsealevelsalongtheseawardboundary(Dayetal2008SmallampNicholls2003)
Sea-level rise can force shifts in wetland vegetation commu-nity composition by altering flooding and salinity regimes (BurdickampMendelssohn 1987 DeLaune Patrick amp Pezeshki 1987 HesterMendelssohn amp McKee 2001 Krauss etal 2009 McKee ampMendelssohn1989)Assalinityincreaseswithsea-levelrisemarshhab-itatswillconverttocommunitiesdominatedbymoresalt-tolerantplantspecies(SharpeampBaldwin2012WarrenampNiering1993)Moreoveranthropogenic restrictions toupslopemigration (EnwrightGriffithampOsland2016)inconjunctionwithsea-levelrisemayresultintheex-pansionof saltmarshesat theexpenseofotherwetland typesyield-ing anoverall shift tomore saline conditions (VisserDuke-SylvesterCarterampBroussard 2013)Changes inwetlandecosystem structuremayeventuallyreflectalteredecological functionandecosystemser-vicesIntidalfreshwaterforestedwetlandsimpactedbysea-levelrisethetransitiontoherbaceousoligohalinemarshresultedingreaternitro-genandphosphorusmineralization fluxesandturnover (NoeKraussLockabyConnerampHupp2013)Similarlythetransitionofherbaceoussaltmarshtomangroveforestsignificantlyalteredecosystemfunctionwith greater carbon sequestration rates and lignin storage rates in mangrovescomparedtosaltmarshes(Bianchietal2013)
Coastalwetlands provide numerous ecosystem services (Barbieretal2011)includingsignificantcarbonstorageinlivingandnon-livingbiomassandinfloodedsoils(McCleodetal2011)Furthermoreunliketerrestrialsoilsthatmaybecomecarbon-saturatedovertime(StewartPaustianConantPlanteampSix2007)coastalwetlandscontinuallyac-cretemineralsedimentsandorganicmattertokeeppacewithsea-levelrise(Reed1995)thusthepotentialforcarbonstorageinwetlandsoilsincreasesovertime(ChmuraAnisfeldCahoonampLynch2003)
Carbon storage in wetlands is the net result of organic matterproduction and organic matter loss for example decomposition
Decompositionoforganicmatterisinfluencedbyinternalandexternaldrivers(GodshalkampWetzel1978)Whenconsideringtheeffectofanultimatedriversuchassea-levelriseonorganicmatterdecomposi-tioninternalandexternaldriverswillhaveindirectanddirectimpactsrespectivelyonthefateoforganicmatter Internaldriversarechar-acteristicsof theorganicmatter itself and includequalitiesofplantmorphologyandchemicalcompositionof theplantmaterial (McKeeampSeneca1982MelilloNaimanAberampLinkins1984)Incontrastexternaldriversofdecompositionarecharacteristicsoftheenviron-mentandincludesoilmicrobeanddetritivorecommunitycomposition(MorriseyBerrierNeubauerampFranklin2014Valielaetal1985)andabiotic conditions suchas soil temperature flooddurationand fre-quencyandsalinity(ReddyampPatrick1975WestonDixonampJoye2006)Therefore sea-level rise has the potential to impact organicmatterdecompositionindirectlybyforcingshiftsinplantcommunitycompositionandlitterquality(internalcontrols)anddirectlythroughalteringsalinityandflooding(externalcontrols)(StaggSchoolmasterKrauss Cormier amp Conner 2017) Furthermore these indirect anddirect impacts are resolved at different spatial and temporal scales(Herbertetal2015NeubauerFranklinampBerrier2013)thereforeitiscriticalthatwequantifybothinternalandexternalcontrolsonor-ganicmatterdecompositionifwehopetoaccuratelypredictthefateoforganicmatterinafuturewithsea-levelrise
Although there has been much recent progress in elucidatingfine-scale mechanisms of soil respiration in response to elevatedsalinity (Chambers Osborne amp Reddy 2013 Chambers Reddy ampOsborne 2011 Neubauer 2013 Neubauer etal 2013 WestonVileNeubauerampVelinsky2011Westonetal2006)westilllackacomprehensiveunderstandingofthemechanismsthatcontrolorganicmatterdecompositionincoastalwetlandsatthelandscapescale(butseeJanouseketal2017WestonNeubauerVelinskyampVile2014)To address thiswemeasured decomposition of in situ litter and astandardizedcarbonsourceacrossalandscape-scalesalinitygradientthatincorporatedchangesinvegetationcommunitytoaddressthefol-lowingresearchquestions(1)Whatdriversinfluenceorganicmatter decompositionalongalandscapesalinitygradientincoastalmarshes(2)Howdo long-term indirect impactsof sea-level risediffer fromshort-termdirectimpactsofsea-levelriseonorganicmatterdecom-positionand(3)Whataretheimplicationsforlong-termcarbonstor-ageinestuarinecoastalwetlandsimpactedbysea-levelrise
2emsp |emspMATERIALS AND METHODS
21emsp|emspStudy sites
Above- and below-ground decomposition was measured in es-tuaries along a landscape-scale (c 65km) salinity gradient that
K E Y W O R D S
carboncellulosedecaycoastalwetlandslandscapelitterdecompositionplantcommunityplant-climateinteractionssea-levelrise
emspensp emsp | emsp657Journal of EcologySTAGG eT Al
incorporatedfresh(0ndash05ppt)oligohaline(05ndash5ppt)mesohaline(5ndash18 ppt) and polyhaline (gt18 ppt) coastal marshes as definedby Cowardin Carter Golet and LaRoe (1979) (Figure1) Due tohightemporalvariationinsalinitywetlandcommunitytypesweredefined not only bymeasured salinity but also by dominant veg-etation species known to be associatedwith specific salinity andhydrologicalregimes(VisserSasserChabreckampLinscombe2002)FreshsitesweredominatedbyPanicum hemitomon and Typha lati-folia oligohaline siteswere dominated by Sagittaria lancifolia and Schoenoplectus americanus mesohaline sites were dominated bySpartina patens and S americanusandpolyhalinesitesweredomi-natedbySpartina alterniflora and Juncus roemerianusWithineachofthefourwetlandtypessixreplicatesiteswereestablishedacrosstwohydrologicbasinsTerrebonneandBaratariaBasinsforatotalof24sites(Figure1Baustianetal2017Staggetal2017)
22emsp|emspResponse variables
221emsp|emspLitter decomposition
Rates of above- and below-ground organic matter decompositionweremeasuredusingthelitterbagtechnique(HackneyampdelaCruz1980) which integrates short- and long-term decomposition pro-cesses associatedwith labile and refractory organicmatter (Valielaetal1985)Litterbagscontainingsite-specificabove-groundbiomassand litterbags containing site-specific below-groundbiomass or lit-terwere installed inthreereplicateplots ineachsiteLivebiomassof each site-specific dominant specieswas collected from a subsetofsiteswithineachwetlandtypeandhydrologicbasin(subsetn=8)in July2014Above-groundbiomassofeachdominantspecieswascollectedfromamonospecificstandclippedat thesoilsurfaceandsortedintoliveanddeadpoolsuponreturningtothelaboratoryTo
collectbelow-groundbiomass in largequantities 20-cmwidetimes30-cmdeepsodswereharvestedfrommonospecificstandsrepresentingeachdominantspeciesThesodsweretransportedbacktothelabora-torywherethebelow-groundbiomasswasrinsedovera1-mmsieveto remove soil particles The remaining macro-organic matter wasseparated into live and dead components Live roots and rhizomesweredistinguishedfromdeadrootsandrhizomesbycolourturgidityandstructuralintegrity(SchubauerampHopkinson1984)Above-andbelow-groundlivebiomasswasallowedtoair-drytoaconstantmassforatleast1weekbeforeplacementinlitterbagsLiveair-driedlitterwas used in place of senesced litter to captureweight loss associ-atedwithinitialdecayprocessessuchasleachingthatwouldhaveal-readyoccurredinsenescedmaterialcollectedfromthefield(McKeeampSeneca1982)Above-groundlitterbagswerepreparedbyfillingmeshbags(20cmlongtimes20cmwidetimes15mmopening)withliveair-driedleafandstemmaterial(20gbag)Below-groundlitterbagswerepre-paredbyfillingmeshbags(8cmlongtimes20cmwidetimes10mmopening)with live air-dried roots and rhizomes (5gbag) Generally above-groundlitterbagshavealargermeshopeningthanbelow-groundlit-terbags(HalupaampHowes1995HemmingaKokampdeMunck1988)toallowforthepassageofsmallandyounginvertebrates(McKeeampSeneca1982)Asubsampleofthe initialair-driedmaterial foreachspecieswasweighedoven-driedat60degCandreweighedtocalculateamoisturecorrectionfactorwhichwasappliedtothestartingmass(w0)ofair-driedlitterusedinsubsequentcalculations
Above- and below-ground litterbag transects were establishedperpendicular to thewater body and included three replicate plotslocated 10 25 and 40m from the shorelineAbove-ground litterb-agsweresecuredonthesoilsurfacewithlandscapepinsandbelow-ground litterbags were inserted into the soil to a depth of 10cmFourlitterbagswereinstalledineachreplicateplot inOctober2014(n=288 above-ground litterbags n=288 below-ground litterbags)
F IGURE 1emspDecompositionstudysiteslocatedalongalandscape-scalesalinitygradientspanningfourwetlandtypesincoastalLouisianaUSA
658emsp |emsp emspenspJournal of Ecology STAGG eT Al
andindividual litterbagswereretrievedfromeachplotatfour inter-vals(136and12monthsafterinstallation)tofollowamodelofex-ponential decayAfter retrieval the above- and below-ground litterbagsweregentlyrinsedwithdeionizedwaterovera1-mmsieveandremaininglitterwasoven-driedforatleast48hrtoaconstantmassat60degC(HalupaampHowes1995)Thelitterwasthenweighedandre-tainedforfurtherchemicalanalysesPercentmassremaining(MR)wascalculatedusingthefollowingequation
where w0isdryweightattimezeroandwtisdryweightattimet(daysafterinstallation)
The proportion of mass remaining over timewas used to esti-mate two parameters that describe the decomposition process (1)thedecayrateorexponentialdecayconstantand(2)theasymptoteornon-decomposable fractionTheexponentialdecayconstantwas derivedusingasinglenegativeexponentialdecaymodel
where X ispercentmassremainingaftertimet (daysafter installa-tion)andminuskistheinstantaneousdecayconstant(perday)(WeiderampLang1982)Additionallyweusedanasymptoticmodel toestimatethenon-decomposablefractionorasymptote
where Caistheasymptoteorfractionofmaterialremaining(WeiderampLang1982)Becausethesingleexponentialdecaymodelprovidedabetterfitfordecayconstantestimatesweonlyusedtheasymptoticmodeltoestimateasymptotesnotdecayconstants
222emsp|emspCellulose decay
Inadditiontolitterdecompositionwealsomeasuredcellulyticactivityusingthecottonstriptechniquewhichprovidesameasureofshort-termlossoflabilecarbon(Maltby1988)Cottonstripsaremadefromartistcanvaswhichiscomprisedof98holocelluloseandbyusingastandardizedcarbonsourcewewereabletoisolateexternalfactorsthat influencemicrobial activity (Mendelssohn etal 1999 SlocumRobertsampMendelssohn2009)
Cottonstripswereinstalledinthreereplicateplotsalongatran-sect parallel to the litterbag transects Below-ground cotton strips(10-cmwidetimes30-cmlong)wereinsertedverticallyintothesoiltoadepthof25cmThecottonstripsweredeployedfourtimesseason-allyandretrievedafter12ndash14daysinthesoildependingonthewatersurfacetemperature(Slocumetal2009)Above-groundcottonstrips(20cmtimes20cm)weredeployedinOctober2015securedtothesoilsurfaceusinglandscapepinsandretrieved14dayslaterThreecot-tonstrips(twoteststripsandonereferencestrip)wereplacedineachreplicatedplotReferencestripsusedtoquantifythetensilestrengthofnon-decomposedmaterialwerehandledexactlythesameastheteststripsbutretrievedimmediatelyafterdeployment
After retrieval cotton strips were rinsed gently with deionizedwatertoremoveallsoilandextraneousmaterialandthecottonstripswereallowedtoair-dryforatleast48hrCottonstripswerecutinto
2-cm substrips along the vertical profile and decomposition of the2-cm substripswasmeasured as tensile strength lost compared tothe reference substrip using a Dillon Quantroltrade Snapshot TensionCompressionMotorizedTestStandtensometerconnectedtoaDillonQuantroltrade Advanced Force Gauge (Slocum etal 2009) Cellulosedecay ratewascalculatedasper cent cellulose tensile strength lostperday(CTSLperday)
whereT is the force (N) requiredto tear thetestsubstripsR is theforce(N)requiredtotearthereferencesubstripsandtistime(days)inthemarsh
23emsp|emspPredictive variables
231emsp|emspExternal drivers
All study sites were located within the 1-km2 boundary of aCoastwide Reference Monitoring Systems station (httplacoastgovcrms2homeaspx) where surface water salinity and surfacewater elevation are measured hourly Marsh surface elevation of15plotswithineachsite (n=360)weresurveyedusingRealTimeKinematicmethodology(GaoAbdel-SalamChenampWojciechowski2005)withaTrimbleR10GNSSSystem(TrimbleNavigationLimitedUSAChenetal2011)andrectifiedtotheNorthAmericanVerticalDatumof1988(NAVD88)usingTrimbleBusinessCenter25soft-ware for data post-processing (Trimble Navigation Limited USA)We usedmarsh elevation data in conjunctionwith surfacewaterelevationdatatocalculateflooddepthanddurationforeachof15plotsineachsite
Discrete soil and porewater sampleswere taken to measure asuiteofenvironmentalparameters inDecember2014Ateachsitetwosoilcores(10-cmdiametertimes30-cmlength)werecollectedneareachofthethreereplicatedplotsalongthebelow-ground litterbagtransect(n=72)Aftercollectionthesoilcoresweresectionedintotwoincrements(0ndash15cmand16ndash30cm)andimmediatelyplacedonice in the fieldand transportedback to the laboratorywhere theywerehomogenizedThefirstcorewasusedforanalysisofsoilbulkdensity (Blake 1965) moisture (Blake 1965) organic mat-ter (OliverLotterampLemcke2001)andelectricalconductivity (ECRhodes1996)
ThesecondsoilcorewasusedtomeasuresoilpH(Thomas1996)soiltotalCNandPsoilextractablenutrients(PO4-PandNH4-N)andotherelementsofinterest(CaCuFeKMgNaNiP)Thehomog-enizedsoilwasdriedtoaconstantweightat60degCgroundinaWileyMill(Model420mesh850μm)andseparatedintoseveralscintil-lationvials formultipleanalysesSoil totalNandtotalCweremea-suredusingaCostechreg4010ElementalCombustionanalyzer(Nelsonamp Sommers 1982 EPAMethod 440) Extractionswere performedforthefollowinganalysessoiltotalP(HClAspilaAgemianampChau1976)PO4-P(Bray-2OlsenampSommers1982)NH4-N(KClKeeneyampNelson1982)andotherparametersofinterest(H2NO3AmericanPublic Health Association 2005a) Soil total P PO4-P samples and
MR= (wt∕w0)times100
X=eminuskt
X=Ca+ (1minusCa)eminuskat
CTSL per day= [1minus (T∕R)times100]∕t
emspensp emsp | emsp659Journal of EcologySTAGG eT Al
NH4-N were measured on a segmented flow AutoAnalyzer (FlowSolution IVAutoAnalyzer O-I Analytical USA EPAMethod 3655EPAMethod 3501)The remaining extractswere analysedwith aninductivelycoupledargonplasmaopticalemissionspectrometer(ICP-OES)(Varian-MPXAgilantUSAAmericanPublicHealthAssociation2005b)
Simultaneously four separate aliquots of porewaterwere col-lectedfromadepthof10cmusingthesipper-tubemethod(VasilasampVasilas2013)Onealiquotofwaterwasused tomeasurepore-water pH (EPA Method 1501) and salinity (EPA Method 1201)The second porewater sample was used to measure porewatertotalNand totalP followingpersulfateoxidation (DrsquoEliaSteudlerampNathaniel1977EbinaTsutsuiampShirai1983)onasegmentedflowAutoAnalyzer (Flow Solution IVAutoAnalyzerO-IAnalyticalUSA)Thethirdaliquotwasfilteredthrougha045-μmfiltertomea-sureNH4-NandPO4-PusingasegmentedflowAutoAnalyzer(FlowSolution IVAutoAnalyzerO-IAnalytical USA EPAMethod3655EPAMethod3501)Thefourthaliquotwasfirstfiltered(45μm)andthenacidifiedtopHlt2tomeasureotherelementsofinterestusingan inductively coupled argon plasma optical emission spectrome-ter (ICP-OES) (Varian-MPX Agilant USA American Public HealthAssociation2005b)
232emsp|emspInternal drivers
Above- and below-ground biomass from each wetland type alongthesalinitygradientwascollectedtocharacterizechemicalcomposi-tionofthelitterinJuly2013and2014InJuly2014subsamplesofinitialabove-andbelow-groundair-driedbiomasscollectedforeachrelevantdominantspecieswithineachwetlandtypewereanalysedfor lignin contentusing theacid-detergent fibreandacid-insolubleash techniques (Van Soest amp Wine 1968) Because insufficientinitial biomass remained for further analyses separate vegetationsamplespreviouslycollectedfromthestudysitesandanalysedfortotalCandtotalNinJuly2013servedasaproxyforthelitterusedin the litterbags In July 2013 above-ground biomasswas clippedat thesoil surface from025-m2quadrats separated into total liveandtotaldeadcomponentsandweighedafterdryingtoaconstantmassat60degC(Mendelssohn1979)Afterabove-groundbiomasswasremovedfromtheplotasharpened10-cmPVCcorerwasusedtocollectbelow-groundbiomass from thecentreof thequadratThecoresweretakentoamaximumdepthof30cmortheentirerootmatthicknessandwerewashedina1-mmsievetoremovesoilpar-ticlesLiverootsandrhizomeswereseparatedfromdeadrootsandrhizomes and the remainingmatrixof deadorganicmaterial baseduponbiomasscolourturgorandbuoyancy(SchubauerampHopkinson1984)Allmaterialwasdriedat60degCtoaconstantmassandweighedAbove-andbelow-groundvegetationsampleswerethengroundinaWileyMill (Model420mesh850μm)oven-driedat60degCandanalysed for totalCand totalNusingaCostechreg 4010ElementalCombustionanalyzer(NelsonampSommers1982EPAMethod440)Only values for live biomass samples were used in subsequent statisticalanalyses
24emsp|emspStatistical analysis
We used a nonlinear regression to estimate decay constants andasymptotes from single exponential decay models and asymptoticmodelsrespectivelyNonlinearregressionmodelsweredevelopedforeach plot in each site (above-groundn=72 below-groundn=72)Onlyestimates frommodels thatsuccessfullyconvergedwereusedinsubsequentstatisticaltestsWeusedamixed-modelANOVAwitharandomizedcompleteblockdesignwithsamplingtocomparevari-ation in response variables (decay constants asymptotes cellulosedecay rates) The fixed effect of wetland type was the treatmenteffect basins represented error associatedwith blocking and threesiteswithineachbasinbywetlandtypetreatmentcombinationrep-resentedsite-levelerrorResponsevariablesweremeasuredinthreeplots within each site which represented sampling error Principalcomponentanalysis(PCA)wasusedtoexplainvariationintheenvi-ronmentalparameterdatasetandananalysisofsimilarity(ANOSIM)wasperformedtodeterminewhethertheprincipalcomponents(PCs)variedsignificantlyamongthetreatmentgroups (wetlandtype)Wecalculated correlation coefficients tomeasure the linear associationbetweenredoxpotentialandPCfactorscoresFinallyweperformedmultiple linear regression analysis using the lm function to identifysignificantpredictorsofdecompositionForeach responsevariableweidentifiedafullmodelapriorithatincludedexplanatoryvariablesofknownimportanceandrelevanceThelitterdecompositionmodelspredictedabove-orbelow-groundlitterdecompositionrateasafunc-tionoflitterqualitysoilandporewaterphysico-chemistryandflood-ing The cellulose decaymodels predicted above- or below-groundcellulose decay rate as a function of soil and porewater physico-chemistryandfloodingWeusedprincipalcomponentfactorsasex-planatoryvariablestorepresentporewaterandsoilphysico-chemistryand flooding Because not all litter quality parameterswere signifi-cantlycorrelatedwithaprincipalcomponentweincludedlitterligninandnitrogencontentasexplanatoryvariablesinthemultipleregres-sionanalysesusing theobserveddata inplaceof the factorscoresThe following analyses were performed in SAS 93 software (SASInstitute Inc 2011) nonlinear regression (proc nlin) ANOVA (procmixed) and correlation analysis (proc corr) The following analyseswereperformedusingRsoftware(RDevelopmentCoreTeam2013)PCAANOSIMandmultiplelinearregression
3emsp |emspRESULTS
31emsp|emspResponse variables
311emsp|emspLitter decomposition
Inallwetlandtypesabove-andbelow-groundlittersignificantlyde-clinedwith time (Table1Figure2)Therewasa significant interac-tionbetweenabove-andbelow-grounddecayrateandwetlandtype(p=0004 df = 3 F=646) however regardless of wetland typeabove-ground litterdecomposed faster thanbelow-ground litter Inbothabove-andbelow-groundlitterpoolsthedecayratewasgreatest
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
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EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
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HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
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HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
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Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
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LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
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Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
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Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp657Journal of EcologySTAGG eT Al
incorporatedfresh(0ndash05ppt)oligohaline(05ndash5ppt)mesohaline(5ndash18 ppt) and polyhaline (gt18 ppt) coastal marshes as definedby Cowardin Carter Golet and LaRoe (1979) (Figure1) Due tohightemporalvariationinsalinitywetlandcommunitytypesweredefined not only bymeasured salinity but also by dominant veg-etation species known to be associatedwith specific salinity andhydrologicalregimes(VisserSasserChabreckampLinscombe2002)FreshsitesweredominatedbyPanicum hemitomon and Typha lati-folia oligohaline siteswere dominated by Sagittaria lancifolia and Schoenoplectus americanus mesohaline sites were dominated bySpartina patens and S americanusandpolyhalinesitesweredomi-natedbySpartina alterniflora and Juncus roemerianusWithineachofthefourwetlandtypessixreplicatesiteswereestablishedacrosstwohydrologicbasinsTerrebonneandBaratariaBasinsforatotalof24sites(Figure1Baustianetal2017Staggetal2017)
22emsp|emspResponse variables
221emsp|emspLitter decomposition
Rates of above- and below-ground organic matter decompositionweremeasuredusingthelitterbagtechnique(HackneyampdelaCruz1980) which integrates short- and long-term decomposition pro-cesses associatedwith labile and refractory organicmatter (Valielaetal1985)Litterbagscontainingsite-specificabove-groundbiomassand litterbags containing site-specific below-groundbiomass or lit-terwere installed inthreereplicateplots ineachsiteLivebiomassof each site-specific dominant specieswas collected from a subsetofsiteswithineachwetlandtypeandhydrologicbasin(subsetn=8)in July2014Above-groundbiomassofeachdominantspecieswascollectedfromamonospecificstandclippedat thesoilsurfaceandsortedintoliveanddeadpoolsuponreturningtothelaboratoryTo
collectbelow-groundbiomass in largequantities 20-cmwidetimes30-cmdeepsodswereharvestedfrommonospecificstandsrepresentingeachdominantspeciesThesodsweretransportedbacktothelabora-torywherethebelow-groundbiomasswasrinsedovera1-mmsieveto remove soil particles The remaining macro-organic matter wasseparated into live and dead components Live roots and rhizomesweredistinguishedfromdeadrootsandrhizomesbycolourturgidityandstructuralintegrity(SchubauerampHopkinson1984)Above-andbelow-groundlivebiomasswasallowedtoair-drytoaconstantmassforatleast1weekbeforeplacementinlitterbagsLiveair-driedlitterwas used in place of senesced litter to captureweight loss associ-atedwithinitialdecayprocessessuchasleachingthatwouldhaveal-readyoccurredinsenescedmaterialcollectedfromthefield(McKeeampSeneca1982)Above-groundlitterbagswerepreparedbyfillingmeshbags(20cmlongtimes20cmwidetimes15mmopening)withliveair-driedleafandstemmaterial(20gbag)Below-groundlitterbagswerepre-paredbyfillingmeshbags(8cmlongtimes20cmwidetimes10mmopening)with live air-dried roots and rhizomes (5gbag) Generally above-groundlitterbagshavealargermeshopeningthanbelow-groundlit-terbags(HalupaampHowes1995HemmingaKokampdeMunck1988)toallowforthepassageofsmallandyounginvertebrates(McKeeampSeneca1982)Asubsampleofthe initialair-driedmaterial foreachspecieswasweighedoven-driedat60degCandreweighedtocalculateamoisturecorrectionfactorwhichwasappliedtothestartingmass(w0)ofair-driedlitterusedinsubsequentcalculations
Above- and below-ground litterbag transects were establishedperpendicular to thewater body and included three replicate plotslocated 10 25 and 40m from the shorelineAbove-ground litterb-agsweresecuredonthesoilsurfacewithlandscapepinsandbelow-ground litterbags were inserted into the soil to a depth of 10cmFourlitterbagswereinstalledineachreplicateplot inOctober2014(n=288 above-ground litterbags n=288 below-ground litterbags)
F IGURE 1emspDecompositionstudysiteslocatedalongalandscape-scalesalinitygradientspanningfourwetlandtypesincoastalLouisianaUSA
658emsp |emsp emspenspJournal of Ecology STAGG eT Al
andindividual litterbagswereretrievedfromeachplotatfour inter-vals(136and12monthsafterinstallation)tofollowamodelofex-ponential decayAfter retrieval the above- and below-ground litterbagsweregentlyrinsedwithdeionizedwaterovera1-mmsieveandremaininglitterwasoven-driedforatleast48hrtoaconstantmassat60degC(HalupaampHowes1995)Thelitterwasthenweighedandre-tainedforfurtherchemicalanalysesPercentmassremaining(MR)wascalculatedusingthefollowingequation
where w0isdryweightattimezeroandwtisdryweightattimet(daysafterinstallation)
The proportion of mass remaining over timewas used to esti-mate two parameters that describe the decomposition process (1)thedecayrateorexponentialdecayconstantand(2)theasymptoteornon-decomposable fractionTheexponentialdecayconstantwas derivedusingasinglenegativeexponentialdecaymodel
where X ispercentmassremainingaftertimet (daysafter installa-tion)andminuskistheinstantaneousdecayconstant(perday)(WeiderampLang1982)Additionallyweusedanasymptoticmodel toestimatethenon-decomposablefractionorasymptote
where Caistheasymptoteorfractionofmaterialremaining(WeiderampLang1982)Becausethesingleexponentialdecaymodelprovidedabetterfitfordecayconstantestimatesweonlyusedtheasymptoticmodeltoestimateasymptotesnotdecayconstants
222emsp|emspCellulose decay
Inadditiontolitterdecompositionwealsomeasuredcellulyticactivityusingthecottonstriptechniquewhichprovidesameasureofshort-termlossoflabilecarbon(Maltby1988)Cottonstripsaremadefromartistcanvaswhichiscomprisedof98holocelluloseandbyusingastandardizedcarbonsourcewewereabletoisolateexternalfactorsthat influencemicrobial activity (Mendelssohn etal 1999 SlocumRobertsampMendelssohn2009)
Cottonstripswereinstalledinthreereplicateplotsalongatran-sect parallel to the litterbag transects Below-ground cotton strips(10-cmwidetimes30-cmlong)wereinsertedverticallyintothesoiltoadepthof25cmThecottonstripsweredeployedfourtimesseason-allyandretrievedafter12ndash14daysinthesoildependingonthewatersurfacetemperature(Slocumetal2009)Above-groundcottonstrips(20cmtimes20cm)weredeployedinOctober2015securedtothesoilsurfaceusinglandscapepinsandretrieved14dayslaterThreecot-tonstrips(twoteststripsandonereferencestrip)wereplacedineachreplicatedplotReferencestripsusedtoquantifythetensilestrengthofnon-decomposedmaterialwerehandledexactlythesameastheteststripsbutretrievedimmediatelyafterdeployment
After retrieval cotton strips were rinsed gently with deionizedwatertoremoveallsoilandextraneousmaterialandthecottonstripswereallowedtoair-dryforatleast48hrCottonstripswerecutinto
2-cm substrips along the vertical profile and decomposition of the2-cm substripswasmeasured as tensile strength lost compared tothe reference substrip using a Dillon Quantroltrade Snapshot TensionCompressionMotorizedTestStandtensometerconnectedtoaDillonQuantroltrade Advanced Force Gauge (Slocum etal 2009) Cellulosedecay ratewascalculatedasper cent cellulose tensile strength lostperday(CTSLperday)
whereT is the force (N) requiredto tear thetestsubstripsR is theforce(N)requiredtotearthereferencesubstripsandtistime(days)inthemarsh
23emsp|emspPredictive variables
231emsp|emspExternal drivers
All study sites were located within the 1-km2 boundary of aCoastwide Reference Monitoring Systems station (httplacoastgovcrms2homeaspx) where surface water salinity and surfacewater elevation are measured hourly Marsh surface elevation of15plotswithineachsite (n=360)weresurveyedusingRealTimeKinematicmethodology(GaoAbdel-SalamChenampWojciechowski2005)withaTrimbleR10GNSSSystem(TrimbleNavigationLimitedUSAChenetal2011)andrectifiedtotheNorthAmericanVerticalDatumof1988(NAVD88)usingTrimbleBusinessCenter25soft-ware for data post-processing (Trimble Navigation Limited USA)We usedmarsh elevation data in conjunctionwith surfacewaterelevationdatatocalculateflooddepthanddurationforeachof15plotsineachsite
Discrete soil and porewater sampleswere taken to measure asuiteofenvironmentalparameters inDecember2014Ateachsitetwosoilcores(10-cmdiametertimes30-cmlength)werecollectedneareachofthethreereplicatedplotsalongthebelow-ground litterbagtransect(n=72)Aftercollectionthesoilcoresweresectionedintotwoincrements(0ndash15cmand16ndash30cm)andimmediatelyplacedonice in the fieldand transportedback to the laboratorywhere theywerehomogenizedThefirstcorewasusedforanalysisofsoilbulkdensity (Blake 1965) moisture (Blake 1965) organic mat-ter (OliverLotterampLemcke2001)andelectricalconductivity (ECRhodes1996)
ThesecondsoilcorewasusedtomeasuresoilpH(Thomas1996)soiltotalCNandPsoilextractablenutrients(PO4-PandNH4-N)andotherelementsofinterest(CaCuFeKMgNaNiP)Thehomog-enizedsoilwasdriedtoaconstantweightat60degCgroundinaWileyMill(Model420mesh850μm)andseparatedintoseveralscintil-lationvials formultipleanalysesSoil totalNandtotalCweremea-suredusingaCostechreg4010ElementalCombustionanalyzer(Nelsonamp Sommers 1982 EPAMethod 440) Extractionswere performedforthefollowinganalysessoiltotalP(HClAspilaAgemianampChau1976)PO4-P(Bray-2OlsenampSommers1982)NH4-N(KClKeeneyampNelson1982)andotherparametersofinterest(H2NO3AmericanPublic Health Association 2005a) Soil total P PO4-P samples and
MR= (wt∕w0)times100
X=eminuskt
X=Ca+ (1minusCa)eminuskat
CTSL per day= [1minus (T∕R)times100]∕t
emspensp emsp | emsp659Journal of EcologySTAGG eT Al
NH4-N were measured on a segmented flow AutoAnalyzer (FlowSolution IVAutoAnalyzer O-I Analytical USA EPAMethod 3655EPAMethod 3501)The remaining extractswere analysedwith aninductivelycoupledargonplasmaopticalemissionspectrometer(ICP-OES)(Varian-MPXAgilantUSAAmericanPublicHealthAssociation2005b)
Simultaneously four separate aliquots of porewaterwere col-lectedfromadepthof10cmusingthesipper-tubemethod(VasilasampVasilas2013)Onealiquotofwaterwasused tomeasurepore-water pH (EPA Method 1501) and salinity (EPA Method 1201)The second porewater sample was used to measure porewatertotalNand totalP followingpersulfateoxidation (DrsquoEliaSteudlerampNathaniel1977EbinaTsutsuiampShirai1983)onasegmentedflowAutoAnalyzer (Flow Solution IVAutoAnalyzerO-IAnalyticalUSA)Thethirdaliquotwasfilteredthrougha045-μmfiltertomea-sureNH4-NandPO4-PusingasegmentedflowAutoAnalyzer(FlowSolution IVAutoAnalyzerO-IAnalytical USA EPAMethod3655EPAMethod3501)Thefourthaliquotwasfirstfiltered(45μm)andthenacidifiedtopHlt2tomeasureotherelementsofinterestusingan inductively coupled argon plasma optical emission spectrome-ter (ICP-OES) (Varian-MPX Agilant USA American Public HealthAssociation2005b)
232emsp|emspInternal drivers
Above- and below-ground biomass from each wetland type alongthesalinitygradientwascollectedtocharacterizechemicalcomposi-tionofthelitterinJuly2013and2014InJuly2014subsamplesofinitialabove-andbelow-groundair-driedbiomasscollectedforeachrelevantdominantspecieswithineachwetlandtypewereanalysedfor lignin contentusing theacid-detergent fibreandacid-insolubleash techniques (Van Soest amp Wine 1968) Because insufficientinitial biomass remained for further analyses separate vegetationsamplespreviouslycollectedfromthestudysitesandanalysedfortotalCandtotalNinJuly2013servedasaproxyforthelitterusedin the litterbags In July 2013 above-ground biomasswas clippedat thesoil surface from025-m2quadrats separated into total liveandtotaldeadcomponentsandweighedafterdryingtoaconstantmassat60degC(Mendelssohn1979)Afterabove-groundbiomasswasremovedfromtheplotasharpened10-cmPVCcorerwasusedtocollectbelow-groundbiomass from thecentreof thequadratThecoresweretakentoamaximumdepthof30cmortheentirerootmatthicknessandwerewashedina1-mmsievetoremovesoilpar-ticlesLiverootsandrhizomeswereseparatedfromdeadrootsandrhizomes and the remainingmatrixof deadorganicmaterial baseduponbiomasscolourturgorandbuoyancy(SchubauerampHopkinson1984)Allmaterialwasdriedat60degCtoaconstantmassandweighedAbove-andbelow-groundvegetationsampleswerethengroundinaWileyMill (Model420mesh850μm)oven-driedat60degCandanalysed for totalCand totalNusingaCostechreg 4010ElementalCombustionanalyzer(NelsonampSommers1982EPAMethod440)Only values for live biomass samples were used in subsequent statisticalanalyses
24emsp|emspStatistical analysis
We used a nonlinear regression to estimate decay constants andasymptotes from single exponential decay models and asymptoticmodelsrespectivelyNonlinearregressionmodelsweredevelopedforeach plot in each site (above-groundn=72 below-groundn=72)Onlyestimates frommodels thatsuccessfullyconvergedwereusedinsubsequentstatisticaltestsWeusedamixed-modelANOVAwitharandomizedcompleteblockdesignwithsamplingtocomparevari-ation in response variables (decay constants asymptotes cellulosedecay rates) The fixed effect of wetland type was the treatmenteffect basins represented error associatedwith blocking and threesiteswithineachbasinbywetlandtypetreatmentcombinationrep-resentedsite-levelerrorResponsevariablesweremeasuredinthreeplots within each site which represented sampling error Principalcomponentanalysis(PCA)wasusedtoexplainvariationintheenvi-ronmentalparameterdatasetandananalysisofsimilarity(ANOSIM)wasperformedtodeterminewhethertheprincipalcomponents(PCs)variedsignificantlyamongthetreatmentgroups (wetlandtype)Wecalculated correlation coefficients tomeasure the linear associationbetweenredoxpotentialandPCfactorscoresFinallyweperformedmultiple linear regression analysis using the lm function to identifysignificantpredictorsofdecompositionForeach responsevariableweidentifiedafullmodelapriorithatincludedexplanatoryvariablesofknownimportanceandrelevanceThelitterdecompositionmodelspredictedabove-orbelow-groundlitterdecompositionrateasafunc-tionoflitterqualitysoilandporewaterphysico-chemistryandflood-ing The cellulose decaymodels predicted above- or below-groundcellulose decay rate as a function of soil and porewater physico-chemistryandfloodingWeusedprincipalcomponentfactorsasex-planatoryvariablestorepresentporewaterandsoilphysico-chemistryand flooding Because not all litter quality parameterswere signifi-cantlycorrelatedwithaprincipalcomponentweincludedlitterligninandnitrogencontentasexplanatoryvariablesinthemultipleregres-sionanalysesusing theobserveddata inplaceof the factorscoresThe following analyses were performed in SAS 93 software (SASInstitute Inc 2011) nonlinear regression (proc nlin) ANOVA (procmixed) and correlation analysis (proc corr) The following analyseswereperformedusingRsoftware(RDevelopmentCoreTeam2013)PCAANOSIMandmultiplelinearregression
3emsp |emspRESULTS
31emsp|emspResponse variables
311emsp|emspLitter decomposition
Inallwetlandtypesabove-andbelow-groundlittersignificantlyde-clinedwith time (Table1Figure2)Therewasa significant interac-tionbetweenabove-andbelow-grounddecayrateandwetlandtype(p=0004 df = 3 F=646) however regardless of wetland typeabove-ground litterdecomposed faster thanbelow-ground litter Inbothabove-andbelow-groundlitterpoolsthedecayratewasgreatest
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
BarbierEHackerSKennedyCKochEWStierACSillimanBR(2011)ThevalueofestuarineandcoastalecosystemservicesEcological Monographs 81169ndash193httpsdoiorg10189010-15101
BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
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Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
OdumW E (1988) Comparative ecology of tidal freshwater and saltmarshes Annual Review of Ecology Evolution and Systematics 19147ndash176httpsdoiorg101146annureves19110188001051
OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
OlsenSRampSommersLE(1982)SoilphosphorusInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and micro-biological properties (pp403ndash430)MadisonWISoilScienceSocietyofAmerica
OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
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TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
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ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
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SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
658emsp |emsp emspenspJournal of Ecology STAGG eT Al
andindividual litterbagswereretrievedfromeachplotatfour inter-vals(136and12monthsafterinstallation)tofollowamodelofex-ponential decayAfter retrieval the above- and below-ground litterbagsweregentlyrinsedwithdeionizedwaterovera1-mmsieveandremaininglitterwasoven-driedforatleast48hrtoaconstantmassat60degC(HalupaampHowes1995)Thelitterwasthenweighedandre-tainedforfurtherchemicalanalysesPercentmassremaining(MR)wascalculatedusingthefollowingequation
where w0isdryweightattimezeroandwtisdryweightattimet(daysafterinstallation)
The proportion of mass remaining over timewas used to esti-mate two parameters that describe the decomposition process (1)thedecayrateorexponentialdecayconstantand(2)theasymptoteornon-decomposable fractionTheexponentialdecayconstantwas derivedusingasinglenegativeexponentialdecaymodel
where X ispercentmassremainingaftertimet (daysafter installa-tion)andminuskistheinstantaneousdecayconstant(perday)(WeiderampLang1982)Additionallyweusedanasymptoticmodel toestimatethenon-decomposablefractionorasymptote
where Caistheasymptoteorfractionofmaterialremaining(WeiderampLang1982)Becausethesingleexponentialdecaymodelprovidedabetterfitfordecayconstantestimatesweonlyusedtheasymptoticmodeltoestimateasymptotesnotdecayconstants
222emsp|emspCellulose decay
Inadditiontolitterdecompositionwealsomeasuredcellulyticactivityusingthecottonstriptechniquewhichprovidesameasureofshort-termlossoflabilecarbon(Maltby1988)Cottonstripsaremadefromartistcanvaswhichiscomprisedof98holocelluloseandbyusingastandardizedcarbonsourcewewereabletoisolateexternalfactorsthat influencemicrobial activity (Mendelssohn etal 1999 SlocumRobertsampMendelssohn2009)
Cottonstripswereinstalledinthreereplicateplotsalongatran-sect parallel to the litterbag transects Below-ground cotton strips(10-cmwidetimes30-cmlong)wereinsertedverticallyintothesoiltoadepthof25cmThecottonstripsweredeployedfourtimesseason-allyandretrievedafter12ndash14daysinthesoildependingonthewatersurfacetemperature(Slocumetal2009)Above-groundcottonstrips(20cmtimes20cm)weredeployedinOctober2015securedtothesoilsurfaceusinglandscapepinsandretrieved14dayslaterThreecot-tonstrips(twoteststripsandonereferencestrip)wereplacedineachreplicatedplotReferencestripsusedtoquantifythetensilestrengthofnon-decomposedmaterialwerehandledexactlythesameastheteststripsbutretrievedimmediatelyafterdeployment
After retrieval cotton strips were rinsed gently with deionizedwatertoremoveallsoilandextraneousmaterialandthecottonstripswereallowedtoair-dryforatleast48hrCottonstripswerecutinto
2-cm substrips along the vertical profile and decomposition of the2-cm substripswasmeasured as tensile strength lost compared tothe reference substrip using a Dillon Quantroltrade Snapshot TensionCompressionMotorizedTestStandtensometerconnectedtoaDillonQuantroltrade Advanced Force Gauge (Slocum etal 2009) Cellulosedecay ratewascalculatedasper cent cellulose tensile strength lostperday(CTSLperday)
whereT is the force (N) requiredto tear thetestsubstripsR is theforce(N)requiredtotearthereferencesubstripsandtistime(days)inthemarsh
23emsp|emspPredictive variables
231emsp|emspExternal drivers
All study sites were located within the 1-km2 boundary of aCoastwide Reference Monitoring Systems station (httplacoastgovcrms2homeaspx) where surface water salinity and surfacewater elevation are measured hourly Marsh surface elevation of15plotswithineachsite (n=360)weresurveyedusingRealTimeKinematicmethodology(GaoAbdel-SalamChenampWojciechowski2005)withaTrimbleR10GNSSSystem(TrimbleNavigationLimitedUSAChenetal2011)andrectifiedtotheNorthAmericanVerticalDatumof1988(NAVD88)usingTrimbleBusinessCenter25soft-ware for data post-processing (Trimble Navigation Limited USA)We usedmarsh elevation data in conjunctionwith surfacewaterelevationdatatocalculateflooddepthanddurationforeachof15plotsineachsite
Discrete soil and porewater sampleswere taken to measure asuiteofenvironmentalparameters inDecember2014Ateachsitetwosoilcores(10-cmdiametertimes30-cmlength)werecollectedneareachofthethreereplicatedplotsalongthebelow-ground litterbagtransect(n=72)Aftercollectionthesoilcoresweresectionedintotwoincrements(0ndash15cmand16ndash30cm)andimmediatelyplacedonice in the fieldand transportedback to the laboratorywhere theywerehomogenizedThefirstcorewasusedforanalysisofsoilbulkdensity (Blake 1965) moisture (Blake 1965) organic mat-ter (OliverLotterampLemcke2001)andelectricalconductivity (ECRhodes1996)
ThesecondsoilcorewasusedtomeasuresoilpH(Thomas1996)soiltotalCNandPsoilextractablenutrients(PO4-PandNH4-N)andotherelementsofinterest(CaCuFeKMgNaNiP)Thehomog-enizedsoilwasdriedtoaconstantweightat60degCgroundinaWileyMill(Model420mesh850μm)andseparatedintoseveralscintil-lationvials formultipleanalysesSoil totalNandtotalCweremea-suredusingaCostechreg4010ElementalCombustionanalyzer(Nelsonamp Sommers 1982 EPAMethod 440) Extractionswere performedforthefollowinganalysessoiltotalP(HClAspilaAgemianampChau1976)PO4-P(Bray-2OlsenampSommers1982)NH4-N(KClKeeneyampNelson1982)andotherparametersofinterest(H2NO3AmericanPublic Health Association 2005a) Soil total P PO4-P samples and
MR= (wt∕w0)times100
X=eminuskt
X=Ca+ (1minusCa)eminuskat
CTSL per day= [1minus (T∕R)times100]∕t
emspensp emsp | emsp659Journal of EcologySTAGG eT Al
NH4-N were measured on a segmented flow AutoAnalyzer (FlowSolution IVAutoAnalyzer O-I Analytical USA EPAMethod 3655EPAMethod 3501)The remaining extractswere analysedwith aninductivelycoupledargonplasmaopticalemissionspectrometer(ICP-OES)(Varian-MPXAgilantUSAAmericanPublicHealthAssociation2005b)
Simultaneously four separate aliquots of porewaterwere col-lectedfromadepthof10cmusingthesipper-tubemethod(VasilasampVasilas2013)Onealiquotofwaterwasused tomeasurepore-water pH (EPA Method 1501) and salinity (EPA Method 1201)The second porewater sample was used to measure porewatertotalNand totalP followingpersulfateoxidation (DrsquoEliaSteudlerampNathaniel1977EbinaTsutsuiampShirai1983)onasegmentedflowAutoAnalyzer (Flow Solution IVAutoAnalyzerO-IAnalyticalUSA)Thethirdaliquotwasfilteredthrougha045-μmfiltertomea-sureNH4-NandPO4-PusingasegmentedflowAutoAnalyzer(FlowSolution IVAutoAnalyzerO-IAnalytical USA EPAMethod3655EPAMethod3501)Thefourthaliquotwasfirstfiltered(45μm)andthenacidifiedtopHlt2tomeasureotherelementsofinterestusingan inductively coupled argon plasma optical emission spectrome-ter (ICP-OES) (Varian-MPX Agilant USA American Public HealthAssociation2005b)
232emsp|emspInternal drivers
Above- and below-ground biomass from each wetland type alongthesalinitygradientwascollectedtocharacterizechemicalcomposi-tionofthelitterinJuly2013and2014InJuly2014subsamplesofinitialabove-andbelow-groundair-driedbiomasscollectedforeachrelevantdominantspecieswithineachwetlandtypewereanalysedfor lignin contentusing theacid-detergent fibreandacid-insolubleash techniques (Van Soest amp Wine 1968) Because insufficientinitial biomass remained for further analyses separate vegetationsamplespreviouslycollectedfromthestudysitesandanalysedfortotalCandtotalNinJuly2013servedasaproxyforthelitterusedin the litterbags In July 2013 above-ground biomasswas clippedat thesoil surface from025-m2quadrats separated into total liveandtotaldeadcomponentsandweighedafterdryingtoaconstantmassat60degC(Mendelssohn1979)Afterabove-groundbiomasswasremovedfromtheplotasharpened10-cmPVCcorerwasusedtocollectbelow-groundbiomass from thecentreof thequadratThecoresweretakentoamaximumdepthof30cmortheentirerootmatthicknessandwerewashedina1-mmsievetoremovesoilpar-ticlesLiverootsandrhizomeswereseparatedfromdeadrootsandrhizomes and the remainingmatrixof deadorganicmaterial baseduponbiomasscolourturgorandbuoyancy(SchubauerampHopkinson1984)Allmaterialwasdriedat60degCtoaconstantmassandweighedAbove-andbelow-groundvegetationsampleswerethengroundinaWileyMill (Model420mesh850μm)oven-driedat60degCandanalysed for totalCand totalNusingaCostechreg 4010ElementalCombustionanalyzer(NelsonampSommers1982EPAMethod440)Only values for live biomass samples were used in subsequent statisticalanalyses
24emsp|emspStatistical analysis
We used a nonlinear regression to estimate decay constants andasymptotes from single exponential decay models and asymptoticmodelsrespectivelyNonlinearregressionmodelsweredevelopedforeach plot in each site (above-groundn=72 below-groundn=72)Onlyestimates frommodels thatsuccessfullyconvergedwereusedinsubsequentstatisticaltestsWeusedamixed-modelANOVAwitharandomizedcompleteblockdesignwithsamplingtocomparevari-ation in response variables (decay constants asymptotes cellulosedecay rates) The fixed effect of wetland type was the treatmenteffect basins represented error associatedwith blocking and threesiteswithineachbasinbywetlandtypetreatmentcombinationrep-resentedsite-levelerrorResponsevariablesweremeasuredinthreeplots within each site which represented sampling error Principalcomponentanalysis(PCA)wasusedtoexplainvariationintheenvi-ronmentalparameterdatasetandananalysisofsimilarity(ANOSIM)wasperformedtodeterminewhethertheprincipalcomponents(PCs)variedsignificantlyamongthetreatmentgroups (wetlandtype)Wecalculated correlation coefficients tomeasure the linear associationbetweenredoxpotentialandPCfactorscoresFinallyweperformedmultiple linear regression analysis using the lm function to identifysignificantpredictorsofdecompositionForeach responsevariableweidentifiedafullmodelapriorithatincludedexplanatoryvariablesofknownimportanceandrelevanceThelitterdecompositionmodelspredictedabove-orbelow-groundlitterdecompositionrateasafunc-tionoflitterqualitysoilandporewaterphysico-chemistryandflood-ing The cellulose decaymodels predicted above- or below-groundcellulose decay rate as a function of soil and porewater physico-chemistryandfloodingWeusedprincipalcomponentfactorsasex-planatoryvariablestorepresentporewaterandsoilphysico-chemistryand flooding Because not all litter quality parameterswere signifi-cantlycorrelatedwithaprincipalcomponentweincludedlitterligninandnitrogencontentasexplanatoryvariablesinthemultipleregres-sionanalysesusing theobserveddata inplaceof the factorscoresThe following analyses were performed in SAS 93 software (SASInstitute Inc 2011) nonlinear regression (proc nlin) ANOVA (procmixed) and correlation analysis (proc corr) The following analyseswereperformedusingRsoftware(RDevelopmentCoreTeam2013)PCAANOSIMandmultiplelinearregression
3emsp |emspRESULTS
31emsp|emspResponse variables
311emsp|emspLitter decomposition
Inallwetlandtypesabove-andbelow-groundlittersignificantlyde-clinedwith time (Table1Figure2)Therewasa significant interac-tionbetweenabove-andbelow-grounddecayrateandwetlandtype(p=0004 df = 3 F=646) however regardless of wetland typeabove-ground litterdecomposed faster thanbelow-ground litter Inbothabove-andbelow-groundlitterpoolsthedecayratewasgreatest
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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AertsRampdeCaluweH(1997)Nutritionalandplant-mediatedcontrolson leaf litterdecompositionofCarex speciesEcology 78 244ndash260httpsdoiorg1018900012-9658(1997)078[0244NAPMCO]20 CO2
Alward R Detling J amp Milchunas D (1999) Grassland vegetationchangesandnocturnalglobalwarmingScience 283118ndash231httpsdoiorg101126science2835399229
AmericanPublicHealthAssociation(2005a)3030EnitricaciddigestionInADEatonampMAFranson(Eds)Standard methods for the exam-ination of water and wastewater (21stedpp325ndash326)WashingtonDCAmericanPublicHealthAssociation
AmericanPublicHealthAssociation(2005b)3120metalsbyplasmaemis-sionspectroscopy(85)InADEatonampMAFranson(Eds)Standard methods for the examination of water and wastewater(21stedpp377ndash386)WashingtonDCAmericanPublicHealthAssociation
emspensp emsp | emsp667Journal of EcologySTAGG eT Al
AspilaKAgemianHampChauS(1976)Asemi-automatedmethodfordeterminationofinorganicorganicandtotalphosphateinsedimentsAnalyst 101187ndash197httpsdoiorg101039an9760100187
Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
BarbierEHackerSKennedyCKochEWStierACSillimanBR(2011)ThevalueofestuarineandcoastalecosystemservicesEcological Monographs 81169ndash193httpsdoiorg10189010-15101
BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
+ uptake inSpartina alterniflora Oecologia 85 375ndash380httpsdoiorg101007BF00320613
Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
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NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
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OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
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OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
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PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
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SAS Institute Inc (2011)Base SASreg 93 procedures guideCaryNCSASInstituteInc
Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp659Journal of EcologySTAGG eT Al
NH4-N were measured on a segmented flow AutoAnalyzer (FlowSolution IVAutoAnalyzer O-I Analytical USA EPAMethod 3655EPAMethod 3501)The remaining extractswere analysedwith aninductivelycoupledargonplasmaopticalemissionspectrometer(ICP-OES)(Varian-MPXAgilantUSAAmericanPublicHealthAssociation2005b)
Simultaneously four separate aliquots of porewaterwere col-lectedfromadepthof10cmusingthesipper-tubemethod(VasilasampVasilas2013)Onealiquotofwaterwasused tomeasurepore-water pH (EPA Method 1501) and salinity (EPA Method 1201)The second porewater sample was used to measure porewatertotalNand totalP followingpersulfateoxidation (DrsquoEliaSteudlerampNathaniel1977EbinaTsutsuiampShirai1983)onasegmentedflowAutoAnalyzer (Flow Solution IVAutoAnalyzerO-IAnalyticalUSA)Thethirdaliquotwasfilteredthrougha045-μmfiltertomea-sureNH4-NandPO4-PusingasegmentedflowAutoAnalyzer(FlowSolution IVAutoAnalyzerO-IAnalytical USA EPAMethod3655EPAMethod3501)Thefourthaliquotwasfirstfiltered(45μm)andthenacidifiedtopHlt2tomeasureotherelementsofinterestusingan inductively coupled argon plasma optical emission spectrome-ter (ICP-OES) (Varian-MPX Agilant USA American Public HealthAssociation2005b)
232emsp|emspInternal drivers
Above- and below-ground biomass from each wetland type alongthesalinitygradientwascollectedtocharacterizechemicalcomposi-tionofthelitterinJuly2013and2014InJuly2014subsamplesofinitialabove-andbelow-groundair-driedbiomasscollectedforeachrelevantdominantspecieswithineachwetlandtypewereanalysedfor lignin contentusing theacid-detergent fibreandacid-insolubleash techniques (Van Soest amp Wine 1968) Because insufficientinitial biomass remained for further analyses separate vegetationsamplespreviouslycollectedfromthestudysitesandanalysedfortotalCandtotalNinJuly2013servedasaproxyforthelitterusedin the litterbags In July 2013 above-ground biomasswas clippedat thesoil surface from025-m2quadrats separated into total liveandtotaldeadcomponentsandweighedafterdryingtoaconstantmassat60degC(Mendelssohn1979)Afterabove-groundbiomasswasremovedfromtheplotasharpened10-cmPVCcorerwasusedtocollectbelow-groundbiomass from thecentreof thequadratThecoresweretakentoamaximumdepthof30cmortheentirerootmatthicknessandwerewashedina1-mmsievetoremovesoilpar-ticlesLiverootsandrhizomeswereseparatedfromdeadrootsandrhizomes and the remainingmatrixof deadorganicmaterial baseduponbiomasscolourturgorandbuoyancy(SchubauerampHopkinson1984)Allmaterialwasdriedat60degCtoaconstantmassandweighedAbove-andbelow-groundvegetationsampleswerethengroundinaWileyMill (Model420mesh850μm)oven-driedat60degCandanalysed for totalCand totalNusingaCostechreg 4010ElementalCombustionanalyzer(NelsonampSommers1982EPAMethod440)Only values for live biomass samples were used in subsequent statisticalanalyses
24emsp|emspStatistical analysis
We used a nonlinear regression to estimate decay constants andasymptotes from single exponential decay models and asymptoticmodelsrespectivelyNonlinearregressionmodelsweredevelopedforeach plot in each site (above-groundn=72 below-groundn=72)Onlyestimates frommodels thatsuccessfullyconvergedwereusedinsubsequentstatisticaltestsWeusedamixed-modelANOVAwitharandomizedcompleteblockdesignwithsamplingtocomparevari-ation in response variables (decay constants asymptotes cellulosedecay rates) The fixed effect of wetland type was the treatmenteffect basins represented error associatedwith blocking and threesiteswithineachbasinbywetlandtypetreatmentcombinationrep-resentedsite-levelerrorResponsevariablesweremeasuredinthreeplots within each site which represented sampling error Principalcomponentanalysis(PCA)wasusedtoexplainvariationintheenvi-ronmentalparameterdatasetandananalysisofsimilarity(ANOSIM)wasperformedtodeterminewhethertheprincipalcomponents(PCs)variedsignificantlyamongthetreatmentgroups (wetlandtype)Wecalculated correlation coefficients tomeasure the linear associationbetweenredoxpotentialandPCfactorscoresFinallyweperformedmultiple linear regression analysis using the lm function to identifysignificantpredictorsofdecompositionForeach responsevariableweidentifiedafullmodelapriorithatincludedexplanatoryvariablesofknownimportanceandrelevanceThelitterdecompositionmodelspredictedabove-orbelow-groundlitterdecompositionrateasafunc-tionoflitterqualitysoilandporewaterphysico-chemistryandflood-ing The cellulose decaymodels predicted above- or below-groundcellulose decay rate as a function of soil and porewater physico-chemistryandfloodingWeusedprincipalcomponentfactorsasex-planatoryvariablestorepresentporewaterandsoilphysico-chemistryand flooding Because not all litter quality parameterswere signifi-cantlycorrelatedwithaprincipalcomponentweincludedlitterligninandnitrogencontentasexplanatoryvariablesinthemultipleregres-sionanalysesusing theobserveddata inplaceof the factorscoresThe following analyses were performed in SAS 93 software (SASInstitute Inc 2011) nonlinear regression (proc nlin) ANOVA (procmixed) and correlation analysis (proc corr) The following analyseswereperformedusingRsoftware(RDevelopmentCoreTeam2013)PCAANOSIMandmultiplelinearregression
3emsp |emspRESULTS
31emsp|emspResponse variables
311emsp|emspLitter decomposition
Inallwetlandtypesabove-andbelow-groundlittersignificantlyde-clinedwith time (Table1Figure2)Therewasa significant interac-tionbetweenabove-andbelow-grounddecayrateandwetlandtype(p=0004 df = 3 F=646) however regardless of wetland typeabove-ground litterdecomposed faster thanbelow-ground litter Inbothabove-andbelow-groundlitterpoolsthedecayratewasgreatest
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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AertsRampdeCaluweH(1997)Nutritionalandplant-mediatedcontrolson leaf litterdecompositionofCarex speciesEcology 78 244ndash260httpsdoiorg1018900012-9658(1997)078[0244NAPMCO]20 CO2
Alward R Detling J amp Milchunas D (1999) Grassland vegetationchangesandnocturnalglobalwarmingScience 283118ndash231httpsdoiorg101126science2835399229
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AmericanPublicHealthAssociation(2005b)3120metalsbyplasmaemis-sionspectroscopy(85)InADEatonampMAFranson(Eds)Standard methods for the examination of water and wastewater(21stedpp377ndash386)WashingtonDCAmericanPublicHealthAssociation
emspensp emsp | emsp667Journal of EcologySTAGG eT Al
AspilaKAgemianHampChauS(1976)Asemi-automatedmethodfordeterminationofinorganicorganicandtotalphosphateinsedimentsAnalyst 101187ndash197httpsdoiorg101039an9760100187
Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
BarbierEHackerSKennedyCKochEWStierACSillimanBR(2011)ThevalueofestuarineandcoastalecosystemservicesEcological Monographs 81169ndash193httpsdoiorg10189010-15101
BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
+ uptake inSpartina alterniflora Oecologia 85 375ndash380httpsdoiorg101007BF00320613
Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
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OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
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OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
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PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
660emsp |emsp emspenspJournal of Ecology STAGG eT Al
intheoligohalinemarshIntheabove-groundlitterpooldecayrateinthepolyhalinemarshwassignificantlygreaterthandecayratesinthefreshandmesohalinemarshes(Figure2a)Incontrastbelow-groundlitterdecayratesdidnotvarysignificantlyamongthefreshmesoha-lineandpolyhalinemarshes(Figure2b)
Therewas a significant interaction between above- and below-ground asymptotes and wetland type (p = 0356 df = 3 F=304Figure2) Above-ground litter decomposition was more complete(smallerasymptote)thanbelow-groundlitterdecompositioninallwet-landtypeswiththeexceptionof theoligohalinemarshwheretheywereequivalentWithin the above-ground litter pool therewasnosignificantvariationinthefractionoflitterremainingamongthefourwetlandtypes (Figure2a) Incontrastbelow-groundthefractionoflitterremainingwassignificantlyhigherinthemesohalinemarshcom-paredtoallotherwetlandtypes(Figure2b)
312emsp|emspCellulose decay
Cellulose decay was greater below-ground than above-ground(Figure3)Furthermoretrendsincellulosedecayalongthelandscapesalinity gradientwere different between above- and below-groundpools (p = 002 df = 3 F=488)Above-groundcellulosedecaywasgreatest in the polyhaline marsh but otherwise similar among theother wetland types Below-ground cellulose decay significantly increasedalongthegradientfromfreshtopolyhalinemarsh
Additionallytherewasasignificantinteractionbetweenwetlandtype and depth (plt0001df=42F=398 FigureS1)At the sur-facecellulosedecayratesweresimilaralongthelandscapegradientAsdepthbelowthesoilsurfaceincreasedtherewasadivergenceincellulosedecayamongthewetlandtypesandoverallratesofdecayweregreaterinthemesohalineandpolyhalinemarshascomparedtothefreshandoligohalinemarsh
32emsp|emspPredictive variables
The PCA generated three PCs that cumulatively explained 59 ofthe variance in the predictive variable dataset (TableS1) The firstPC(PC1mdashPhysico-chemical)explained39ofthevarianceandwasdefinedbyporewaterandsoilphysico-chemicalpropertiesincludingtemperaturesalinityandnutrientparametersAnnualsurfacewatertemperaturewas positively associatedwith PC1 (R2=65) aswereporewaterandsoilsalinityparameterssuchasporewaterandsoilEC(R2=90and 89 respectively)SoilnutrientparameterssuchassoiltotalnitrogenandtotalphosphoruswerenegativelycorrelatedwithPC1 (R2=minus90andminus67respectively)ThesecondPC (PC2mdashLignin)explainedc13ofthevariationandwasdefinedbylignincontentofabove-ground(leaf)andbelow-ground(root)litterLeaflignincontentwaspositivelycorrelatedwithPC2(R2=55)androotlignincontentwasnegativelycorrelatedwithPC2(R2=minus55)whereasleafandrootlitternitrogencontentwerenotsignificantlycorrelatedwith thisoranyotherPC
The third PC (PC3ndashFlooding) explained 7 of the databasevariance andwas defined by elevation and flood duration parame-tersWetland surface elevationwas negatively correlatedwith PC3(R2=minus55)andannualpercenttimefloodedwaspositivelycorrelatedwithPC3(R2=54)
TherewasaseparationamongthewetlandtypesalongboththePC1(Physico-chemical)andPC2(Lignin)axes(R = 212 p = 001 and R=092 p=001 for PC1 and PC2 respectively)As expected thefour wetland types separated by salinity (Figure4ab) Additionallywetlandstypeswithhigh leaf lignincontentalsohadlowroot lignincontent(Figure4ac)
Due tomissing redoxpotential data thisparameterwasnot in-cludedinthePCAorinthesubsequentmultipleregressionanalysesHowever redox potential varied significantly among the wetland
Wetland type Pool Parameter Estimate SE t- value p- value
Fresh Above k 0003 910E-05 32 lt0001
Oligohaline Above k 0005 000041 131 lt0001
Mesohaline Above k 0003 000012 208 lt0001
Polyhaline Above k 0004 000012 337 lt0001
Fresh Below k 0002 000011 156 lt0001
Oligohaline Below k 0003 000024 129 lt0001
Mesohaline Below k 0001 00001 128 lt0001
Polyhaline Below k 0001 00001 133 lt0001
Fresh Above a 2199 627 351 00008
Oligohaline Above a 2302 543 424 lt0001
Mesohaline Above a 2197 711 309 003
Polyhaline Above a 767 941 082 42
Fresh Below a 4413 627 704 lt0001
Oligohaline Below a 3185 521 611 lt0001
Mesohaline Below a 6174 543 1137 lt0001
Polyhaline Below a 4418 595 743 lt0001
TABLE 1emspNonlinearregressionestimatesofsingleexponentialdecayconstants(minuskperday)andasymptotes (a)forabove-andbelow-groundlitterdecomposition
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
BarbierEHackerSKennedyCKochEWStierACSillimanBR(2011)ThevalueofestuarineandcoastalecosystemservicesEcological Monographs 81169ndash193httpsdoiorg10189010-15101
BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
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Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
OdumW E (1988) Comparative ecology of tidal freshwater and saltmarshes Annual Review of Ecology Evolution and Systematics 19147ndash176httpsdoiorg101146annureves19110188001051
OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
OlsenSRampSommersLE(1982)SoilphosphorusInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and micro-biological properties (pp403ndash430)MadisonWISoilScienceSocietyofAmerica
OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
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ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp661Journal of EcologySTAGG eT Al
types andwas highest in the freshmarsh and lowest in themeso-halineandpolyhalinemarshes(plt0001df = 3 F=5282Figure5)Additionallyredoxpotentialwashighlycorrelatedwithseveralwell-characterized parameters associated with PC1 (Physico-chemical)such as porewater EC and porewater sulphur (R2=minus63 plt0001R2=minus46p=002respectively)
33emsp|emspMultiple regression analysis
Initialnitrogencontentwas theonly significantpredictorofabove-groundlitterdecomposition(Table2)whichincreasedwithincreasinglitternitrogencontent(Figure6a)Initiallignincontentwasasignifi-cantpredictorofbelow-groundlitterdecomposition(Table2)whichdeclinedwithincreasinglignincontent(Figure6b)
NeitherPC1(Physico-chemical)norPC3(Flooding)hadasignifi-canteffectonabove-groundcellulosedecay(Table2)IncontrastPC1(Physico-chemical) andPC3 (Flooding)were importantpredictorsof
below-groundcellulosedecay(Table2)whichincreasedwithincreas-ingsalinityand floodinganddecreasingsoilnutrientconcentrations(Figure7ab)
4emsp |emspDISCUSSION
To improveourunderstandingofhoworganicmatterdecomposi-tionandthefateofcarbonincoastalwetlandswillbeimpactedbysea-level rise we identified the internal and external drivers thatinfluencedecompositionincoastalwetlandsacrossanestuarinesa-linitygradientspanningfreshtopolyhalinewetlandtypes Internaldriverssuchaslitterqualityarecharacteristicsoftheorganicmat-ter itselfwhereas external drivers such as hydrologic conditionsare characteristics of the environment (Aerts 1997 Webster ampBenfield 1986) and their effects on decomposition may be ex-pressed through both direct and indirect pathways For example
F IGURE 2emspEstimatesof(a)above-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativeabove-groundbiomassremainingovertime(b)below-groundlitterdecayconstantsandasymptotesalongthelandscapegradientand(inset)relativebelow-groundbiomassremainingovertimeBarsrepresentmeans(n=18)anderrorbarsrepresentSEsCapitallettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongasymptotemeansfrombothabove-andbelow-groundpoolsLowercaselettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsamongdecayconstantmeansfrombothabove-andbelow-groundpools(FisherrsquosProtectedLSDα=005)
(a)
(b)
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
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forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
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DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
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HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
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HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
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Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
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LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
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Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
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670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
662emsp |emsp emspenspJournal of Ecology STAGG eT Al
sea-level rise can impact soil organic matter decomposition indi-rectly through changes in internal drivers such as plant commu-nity composition and litter qualitywhich control litter decay rate(StaggSchoolmasterKraussetal2017) Inthisstudywefoundthatdespitesignificantvariationinenvironmentalconditionsalongthisgradientexternaldriversincludingporewatersalinityandflooddurationhadnosignificantpredictivecapacityforeitherabove-orbelow-ground litterdecompositionThereforeour results indicatethattheindirectpathwaymediatedthroughchangesinlitterqualityan internaldriverwasmore important incontrolling litterdecom-positionthandirecteffectsofexternaldriversalongthislandscapegradient
Previous research has documented variation in lignin contentamongdifferentwetlandplantspecies(Buth1987GuoLuTongampGuohua2008)andourmeasurementsoflitterlignincontentforfresholigohalinemesohalineandpolyhalinespeciesweresimilartothosereported in the literature (Table3) However decay constants frommixed-specieslittermaterialwilldiffersignificantlycomparedtolittercomprisedofasinglespecies(ChapmanNewmanHartSchweitzerampKoch2013)Thereforeinsitumeasurementsoflittermixturesthatrepresentthevegetationcommunityarecriticalforachievingaccurateestimates of litter decay and identifying patterns of decompositionamongdifferentwetlandtypes
Because lignincontentcandiffersignificantlybetweentwospe-cieswithin the samewetland type or salinity zone it is difficult toidentifyuniversal patternsof lignin content alonga landscape-scalesalinity gradient Furthermore changes in plant diversity along thelandscapegradientmayimpactratesofdecompositionOdum(1988)observedgreaterplantdiversity infreshmarshescomparedtomoresalinemarsheswhichmayaffecttheproportionofdifferentspeciesand overall litter quality in a litter mixture Very few studies havecompared litter quality and decomposition along a salinity gradientthatincorporateschangesincomposition(GallagherKibbyampSkirvin
1984LopesMartinsRicardoRodriguesampQuintino2011ScartonDayampRismondo2002Windham2001)andasfarasweknowthisisthefirststudytoquantifylitterdecompositiondynamicsofdiffer-entwetlandtypesacrosstheentirecoastalmarsh landscapesalinitygradientOdumrsquos (1988) comparative review of freshvs polyhalinetidal marshes reports that freshwater macrophytes from the lowerintertidal zone such asSagittaria latifolia tend to have lower lignincontenthighernitrogencontentandhigherdecayratescomparedto
F IGURE 3emspCellulosedecayamongdifferentwetlandtypesBarsrepresentmeans(n=540)anderrorbarsrepresentSEsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
F IGURE 4emspPrincipalComponentAnalysisbiplotsofobservationprojectionsorfactorscoresincomponentspaceforallcomparisonsbetween(a)principalcomponent(PC)1andPC2(b)PC1andPC3and(c)PC2andPC3IneachplotfactorscoresarecolouredbywetlandtypeAsubsetofhighlycorrelatedvectorsfromeachPCoverlaythefactorscores
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
2 (L
igni
n)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
minus6 minus4 minus2 0 2 4 6
minus6minus4
minus20
24
6
PC2 (Lignin)
PC
3 (F
lood
ing)
FreshOligohaline Mesohaline Polyhaline
(a)
(b)
(c)
PC1 ( )
PC1 ( )
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
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Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
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DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
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MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
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NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
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OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
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OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
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PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
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SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp663Journal of EcologySTAGG eT Al
polyhalineorsaltmarshspeciesIncontrastfreshwatermacrophytesfrom the upper intertidal such asT latifolia more closely resemble typicalsaltmarshplantsintheirligninandnitrogencontentandexhibitslowerratesofdecaythanplantsfromthelowerintertidalfreshzoneInsupportofOdumrsquosconclusionswefoundthatlitterdecompositionwas greatest in the oligohalinemarsheswhichwere dominated byS lancifolia and S americanusandalsohadthelowestlignincontentThefreshmarshdominatedbyT latifolia and P hemitomon was similar inlignincontentanddecayratetothemesohalinemarshesdominatedby S patensandthepolyhalinemarshesdominatedbyS alterniflora and J roemerianus Thus although landscape-scale salinity patternsoflignincontentandlitterdecompositionarelargelyspecies-specific
(AertsampdeCaluwe1997)itisclearthatsea-levelrisehasthepoten-tialtoalterthequalityofcarbonandindirectlyimpactdecompositionalongthisgradient
Similarlyinitiallitterqualityintheformofnitrogencontentwasthebestpredictorof above-ground litter decomposition (MarinucciHobbie amp Helfrich 1983 Taylor Parkinson amp Parsons 1989)Althoughsomeresearchidentifiestheratiooflignin-to-nitrogeninini-tiallitterqualityasanimportantpredictorofdecomposition(MelilloAberampMuratore1982Valielaetal1984)ourresultsindicatethatonlyoneofthesevariableswasasignificantpredictoreithernitrogencontent or lignin content of above- or below-ground litter decom-positionrespectivelyLikewiseastudybyMelilloNaimanAberandEshleman(1983)identifiedeitherligninaloneorincombinationwithnitrogencontentasasignificantpredictorofdecompositionThesig-nificanceofonepredictoroveranothermaybeduetointeractionsbe-tweeninitiallitterqualityandenvironmentalconditionsIngeneralifexogenousnitrogen(egfromsoilorwatercolumn)isreadilyavailabletomicrobesandorinitiallitterlignincontentishightheninitiallitternitrogencontentmayhave little impactondecayrate (Melilloetal1982 1984) Interestingly despite these differences among above-andbelow-groundlittercontentthepatternofdecayalongtheland-scapegradientwassimilarwiththegreatestdecompositionoccurringin the oligohaline marsh Although salinity is a known regulator ofplantnitrogendynamics (BradleyampMorris1991Morris1980)wedidnotobserveasimplelineardeclineinlitterqualitywithincreasingsalinityThusitisclearthatlitterdecompositioniscontrolledthroughan indirectpathwaymediatedby internaldriversbutmoreresearchisneededtoidentifytheultimatedriversthatgenerateoptimallitterqualityforenhanceddecayintheoligohalinemarsh
To characterize the direct effects of sea-level rise ondecompo-sitionwe controlled for the influenceof litter qualitybymeasuringthe decay rate of a standard carbon source cellulose across thelandscape-scalesalinitygradient(Mendelssohnetal1999)Celluloseisalabilecompoundthatrapidlydecaysduringtheinitialphasesofde-compositionandservesasareadilyavailablefuelformicrobialactivity
TABLE 2emspResultsofmultiplelinearregressionanalysisforlitterdecompositionandcellulosedecay
Response variable Predictive variable Parameter estimate SE t- value p- value Model R2
Above-groundlitter PC1 minus177E-05 565E-05 minus0314 755 121
Decomposition PC3 minus495E-05 131E-04 minus0378 707
LeafN 00003 104E-03 268 009
LeafLignin minus736E-05 218E-04 minus0338 736
Below-groundlitter PC1 431E-05 338E-05 127 207 395
Decomposition PC3 507E-05 676E-05 0750 456
RootN 353E-04 313E-04 113 265
RootLignin minus217E-04 363E-05 minus598 110E-07
Above-ground PC1 0042 0032 130 198 027
Cellulose decay PC3 minus0021 0075 minus0280 780
Below-ground PC1 0039 0012 324 002 195
Cellulose decay PC3 0066 0028 236 021
plt05plt01plt001
F IGURE 5emspVariationinsoilredoxpotentialalonglandscapegradientBoxplotboundariesclosesttozerorepresentthe25thpercentilethelinewithintheboxesindicatesthemedianandboundariesfarthestfromzerorepresentthe75thpercentile(n=90)Whiskersindicatethe90thand10thpercentilesBlackdotsrepresentoutlyingpointsLettersdenotestatisticalsignificanceofpost-hocmultiplecomparisonsofmeans(FisherrsquosProtectedLSDα=005)
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
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forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
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DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
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HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
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HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
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Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
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LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
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Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
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670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
664emsp |emsp emspenspJournal of Ecology STAGG eT Al
(Hodson Chrsitian amp Maccubbin 1984) Therefore in addition toidentifyingexternalcontrolsondecaywewerealsoabletocharac-terizethedecompositiondynamicsoftheisolatedlabilecarbonpool
We found that below-ground cellulosedecay increasedwith in-creasingsalinitywhichsupportsfindingsfromrecentstudiesthatsoilrespirationisstimulatedbysalinityinshort-termexposuresthatdonotincorporatechangesincarbonsource(Chambersetal2011Westonetal2006)Whileincreasingsalinitycanhavedirectimpactsonor-ganicmattermineralizationthroughalteringthesoilchemicalcompo-sitionandreleasingpreviouslysoil-boundorganiccarbon(DouPingGuoampJorgenson2005)thepatternofcellulosedecayalongthissa-linitygradientwaslikelyinfluencedbydifferencesamongthemicrobialcommunities(Chambersetal2013)Assalinitycontinuestoincreasesulphate reducersout-competemethanogensandoverall anaerobicmetabolism isgreaterwhensulphate is thedominant terminalelec-tronacceptor(Sutton-GrierKellerKochGilmourampMegonigal2011Westonetal2006)
In contrast to salinity soil nutrients were negatively correlatedwith below-ground cellulose decay Although Mendelssohn etal
(1999)foundthatsoilnutrientshadasignificantpositiveinfluenceoncellulose decay in a Phragmites australis-dominatedwetlandthistrendisnotuniversalamongallwetlandtypesForexamplethereviewbyRybczyk Garson andDay (1996) illustrates varying impacts of soilnutrientsonsoilorganicmatterdecompositionEvensoitisunlikelythathighsoilnutrientswoulddirectlyinhibitcellulosedecayRatherweproposethatthestimulatoryeffectofelevatedsalinityandgreatersulphate availability overcame the potential negative effects of lowsoilnutrientconcentrations
Floodingwasalsoa strongpredictorofdecomposition andhada direct positive effect on below-ground cellulose decay Althoughgreaterflooddurationcanleadtoanaerobicsoilconditions(GambrellampPatrick1978Ponnamperuma1984)whichcan limit the rateofdecomposition (Day amp Megonigal 1993 McKee amp Seneca 1982WhiteampTrapani1982)decompositionisnotalwaysslowerunderan-aerobicconditionsForexampleKirwanLangleyGuntenspergenand
F IGURE 6emspLinearregressionof(a)above-groundlitterdecompositionandlitternitrogencontentand(b)below-groundlitterdecompositionandlitterlignincontentFresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
F IGURE 7emspLinearregressionofbelow-groundcellulosedecayand(a)PC1(Physico-chemical)and(b)PC3(Flooding)Fresholigohalinemesohalineandpolyhalinewetlandtypesdifferentiatedbyshapesymbols
(a)
(b)
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
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GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
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HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
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HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
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HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
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KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
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LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
OdumW E (1988) Comparative ecology of tidal freshwater and saltmarshes Annual Review of Ecology Evolution and Systematics 19147ndash176httpsdoiorg101146annureves19110188001051
OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
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OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
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ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
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Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
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WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
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Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
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SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp665Journal of EcologySTAGG eT Al
Megonigal(2013)observedastimulatoryfloodingeffectonrootandrhizomedecompositionFurthermore soil redoxpotentialalong thislandscapegradientwasmorecloselycorrelatedwithporewatersalin-itythanwithfloodduration(PwECR2=minus62plt0001AnnFloodR2=minus39p=01) indicating that the stimulating effect of floodingwasnotstronglyassociatedwithanaerobicconditionsThereforeweproposethatthepositiverelationshipbetweenfloodingandcellulosedecayillustratesthewell-documentedobservationthatmicrobialac-tivity ismoisture-limited (FrascoampGoode 1982HalupaampHowes
1995NewellArsuffiampPalm1996ReiceampStiven1983)at leastinthetop20cmofthesoilprofileAtfurtherdepthscellulosedecaybelowthesoilsurfacewaslikelyoxygenlimitedassoilsbecomemorereduced with increasing depth (Maltby 1988 Schipper amp Reddy1995)Similartoourfindingslowoxygenavailabilityhasbeeniden-tifiedasaprimaryinhibitorofcellulosedecayatdepthsbelow22cm(Mendelssohnetal1999)
Surprisingly none of the environmental drivers we measuredhad predictive capacity for above-ground cellulose decayAlthough
TABLE 3emspLitterlignincontentofdominantspeciesfromeachwetlandtypeLitterconditionidentifiedaslive(L)dead(D)orunknown(U)
Species Litter type Lignin content () Study
Typha latifolia Leaves 122L Currentstudy
58L MoranampHodson(1989)
395ndash427D WelschampYavitt(2003)
182D PoideNeiffNeiffampCasco (2006)
Roots 73L Currentstudy
Panicum hemitomon Leaves 64ndash73L Currentstudy
64L MoranampHodson(1989)
59D OsborneInglettampReddy(2007)
Roots 88ndash122L Currentstudy
Sagittaria lancifolia Leaves 77ndash77L Currentstudy
18U Laursen(2004)
Roots 54ndash74L Currentstudy
26U Laursen(2004)
Schoenoplectus americanus Leaves 79ndash89L Currentstudy
205D BallampDrake(1997)
Roots 47ndash75L Currentstudy
1443ndash2650L SaundersMegonigalampReynolds(2006)
Spartina patens Leaves 78ndash92L Currentstudy
142D BallampDrake(1997)
Roots 148ndash186L Currentstudy
2695ndash3041L Saundersetal(2006)
Juncus roemerianus Leaves 99L Currentstudy
6U Benneretal(1987)
Roots 137L Currentstudy
51U Benneretal(1987)
Spartina alterniflora Leaves 55ndash57L Currentstudy
151L MaccubbinampHodson(1980)
131ndash168L Hodsonetal(1984)
117U Wilson(1985)
11ndash12D WilsonBuchsbaumValielaampSwain(1986)
43ndash61U Benneretal(1987)
Roots 137ndash152L Currentstudy
122ndash193U Hodsonetal(1984)
93U Benneretal(1987)
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
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GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
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StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
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WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
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Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
666emsp |emsp emspenspJournal of Ecology STAGG eT Al
above-groundcellulosedecayvariedsignificantlyacrossthelandscape-scalesalinitygradient(higherinpolyhalinemarsh)salinitypersewasnotasignificantpredictorofdecay(sensuMendelssohnetal1999)Several recentstudieshave illustratedthatsalinitycan indirectlyaf-fect soil respiration throughchanges inmicrobial function resultinginhigherratesofcarbonmineralizationathighersalinities(Chambersetal2011Neubauer2013Sutton-Grieretal2011Westonetal2006)Thuswehypothesizethatanunidentifiedmediatingfactorthatvarieswithwetlandtypesuchasmicrobialfunction(CaponeampKiene1988) is regulating cellulose decayWe suggest that future studiesinclude focusedmeasuresofmicrobial structure and function alongthislandscape-scalegradienttoconfirmthemechanismofindirectef-fectsofsalinityoncellulosedecay(HopfenspergerBurginSchoepferampHelton2014Morriseyetal2014NeubauerGivlerValentineampMegonigal2005)
Insummaryourstudyshowedthat the indirecteffectofsea-levelriseonlitterdecompositionwasmediatedthroughchangesinplantcommunitycompositionand litterqualitywhich resulted indecliningratesoflitterdecompositionalongthegradientfromoli-gohalinetopolyhalinemarshesHoweverwhenwecontrolledforchangesinlitterqualitywefoundthatincreasingsalinityandflood-ingstimulateddecayoflabilecarbon(cellulose)Wehaveidentifiedtwomechanismsoforganicmatterlossoperatingatdifferenttem-poralscalesthatprovideinsighttothepotentialforlong-termcar-bonstorageassea-levelrisesOurresultsindicatethatassealevelrises initial direct effectsof salinitywill stimulatedecayof labilecarbonbutovertimeasvegetationcommunitycompositionshiftstomoresalinewetlandtypes litterdecay (decayofrefractilecar-bon)willdeclineyieldinggreaterpotential for long-termsoilcar-bonstoragethroughnetaccretion(LoomisampCraft2012)Recentstudieshavehighlightedtheimportanceofscaleinconsideringtheinfluence of sea-level rise on carbon loss fromwetland systems(Herbertetal2015Neubaueretal2013)Ourresearchprovidesanexampleofhowmultiplemechanismsofcarbon lossoperatingatdifferentscalescanyielddifferentratesandpatternsoforganicmatter decompositionwhich is relevant not only in coastalwet-landsbutalsoinotherecosystemssuchasgrasslandsshrublandsandforestswhereplant-mediatedresponsestoclimatechangewillhavesignificant impactsoncarbondynamics (JobbagyampJackson2000)
ACKNOWLEDGEMENTS
The authors acknowledge themany people who assisted in fieldsamplecollectionandsampleprocessingAdaDizEvanBergeronKelly Darnell Lindsey Hebert Samantha Humphrey JamalMathurinAlyssaMitchellLelandMossBrettPattonSaraiPiazzaCaitlinPinsonatJacyReynoldsJacksonRollingsandRachelVillaniWe thank Thomas Blanchard and Sara Gay at Louisiana StateUniversityWetlandBiogeochemistryAnalyticalServicesandUttamKumarSahaandDavidParksatUniversityofGeorgiaCooperativeExtension for performing chemical analyses We are grateful toChristopherSwarzenski forhishelp insiteselectionBrettPatton
for rectifyingelevationdatasetsLelandMoss fordevelopmentofFigure1LaurenLeonpacherfordevelopmentofTable3andmanu-scripteditingWealsothankJoshuaJonesChristopherSwarzenskiandanonymouspeersfortheirreviewofthismanuscriptThisre-searchwasfundedbytheUSGeologicalSurveyClimateResearchand Development Program US Geological Survey EcosystemsProgram the US Geological Survey LandCarbon program theScienceandEngineeringProgramofTheWaterInstituteoftheGulfwith funds fromtheLouisianaCoastalProtectionandRestorationAuthority (CPRA) and the Baton Rouge Area Foundation (BRAF)andtheRestoretheMississippiRiverDeltaCampaignviaCoalitionto Restore Coastal Louisiana (CRCL) Any use of trade firm orproductnamesisfordescriptivepurposesonlyanddoesnotimply endorsementbytheUSGovernment
AUTHORrsquoS CONTRIBUTIONS
CLSMMBandCLPconceivedtheideasanddesignedmethod-ology CLSMMB CLP TJBC andCTH collected the dataCLSMMBandCTHanalysedthedataCLSledthewritingofthe manuscript All authors contributed critically to the drafts andgavefinalapprovalforpublication
DATA ACCESSIBILITY
Allof thesupportingdatapresented in thispaperhavebeenpubli-callyarchivedatsciencebasegovhttpsdoiorg105066f7639mvk(StaggBaustianPerryCarruthersampHall2017)
ORCID
Camille L Stagg httporcidorg0000-0002-1125-7253
Melissa M Baustian httporcidorg0000-0003-2467-2533
Courtney T Hall httporcidorg0000-0003-0990-5212
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GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
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KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
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ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
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SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp667Journal of EcologySTAGG eT Al
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Ball A amp Drake B (1997) Short-term decomposition of litter pro-duced by plants grown in ambient and elevated atmosphericCO2 concentrations Global Change Biology 3 29ndash35 httpsdoiorg101046j1365-2486199700091x
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BaustianMMStaggCLPerryCLMossLCCarrutherTJBampAllisonM(2017)Relationshipsbetweensalinityandshort-termsoilcarbonaccumulationratesfrommarshtypesacrossalandscapeintheMississippiRiverDeltaWetlands 37313ndash324
BennerRFogelMSpragueEampHodsonR (1987)Depletionof13C inligninanditsimplicationsforstablecarbonisotopestudiesNature 329708ndash710httpsdoiorg101038329708a0
Bianchi T Allison M Zhao J Li X Comeaux R S Feagin R AWasanthaKulawardhanaR(2013)Historicalreconstructionofman-grove expansion in theGulf ofMexico Linking climate changewithcarbonsequestration incoastalwetlandsEstuarine Coastal and Shelf Science 1197ndash16httpsdoiorg101016jecss201212007
BlakeG(1965)Methods of soil analysisInCBlackDEvansLEnsmingerJWhiteampFClark(Eds)MadisonWIAmericanSocietyofAgronomy
BradleyPampMorrisJ(1991)TheinfluenceofsalinityonthekineticsofNH4
+ uptake inSpartina alterniflora Oecologia 85 375ndash380httpsdoiorg101007BF00320613
Burdick D ampMendelssohn I (1987)Waterlogging responses in duneswaleandmarshpopulationsofSpartina patensunderfieldconditionsOecologia 74321ndash329httpsdoiorg101007BF00378924
Buth G (1987) Decomposition of roots of three plant communitiesin a Dutch salt marsh Aquatic Botany 29 123ndash138 httpsdoiorg1010160304-3770(87)90091-X
CaponeDampKieneR(1988)Comparisonofmicrobialdynamicsinma-rineandfreshwatersedimentsContrastsinanaerobiccarboncatabo-lism Limnology and Oceanography 33725ndash749
Chambers LOsborneTampReddyK (2013) Effectof salinity-alteringpulsingeventsonsoilorganiccarbonlossalonganintertidalwetlandgradient A laboratory experiment Biogeochemistry 115 363ndash383 httpsdoiorg101007s10533-013-9841-5
Chambers L Reddy K amp Osborne T (2011) Short-term response ofcarboncyclingtosalinitypulses ina freshwaterwetlandSoil Science Society of America Journal 75 2000ndash2007 httpsdoiorg102136sssaj20110026
ChapmanSNewmanGHartSSchweitzerJAKochGW(2013)Leaflittermixtures altermicrobial community developmentMechanismsfornon-additiveeffectsinlitterdecompositionPLoS ONE 81ndash9
ChenXAllisonTCaoWFergusonKGruumlnigSampGomezVhellipTablotN(2011)TrimbleRTXaninnovativenewapproachfornetworkRTKInProceedings of the 24th international technical meeting of the satellite division of the institute of navigation (ION GNSS 2011)pp2214ndash2219PortlandOR
ChmuraGAnisfeldSCahoonDampLynchJ(2003)Globalcarbonse-questrationintidalsalinewetlandsoilsGlobal Biogeochemical Cycles 17 1ndash12
CowardinLMCarterVGoletFCampLaRoeET(1979)ClassificationofwetlandsanddeepwaterhabitatsoftheUnitedStatesFWSOBS-7931USFishandWildlifeServiceWashingtonDC
DayJChristianRBoeschDYaacutentildeez-ArancibiaAMorrisJTwilleyRRhellip StevensonC (2008)Consequencesof climate changeon theecogeomorphologyofcoastalwetlandsEstuaries and Coasts 31477ndash491httpsdoiorg101007s12237-008-9047-6
DayFampMegonigalJ (1993)Therelationshipbetweenvariablehydro-period production allocation and belowground organic turnover in
forestedwetlandsWetlands 13 115ndash121 httpsdoiorg101007BF03160871
DeLaune R PatrickW Jr amp Pezeshki S (1987) Foreseeable floodinganddeathofcoastalwetlandforestsEnvironmental Conservation 14 129ndash133httpsdoiorg101017S0376892900011486
DrsquoElia C F Steudler P A amp Nathaniel C (1977) Determinationof total nitrogen in aqueous samples using persulfate digestionLimnology and Oceanography 22 760ndash764 httpsdoiorg104319lo19772240760
DouF PingCGuo L JorgensonT (2005) Estimating the impactofseawateron theproductionof soilwater-extractableorganiccarbonduring coastal erosion Journal of Environmental Quality 37 2368ndash2374httpsdoiorg102134jeq20070403
Ebina J Tsutsui T amp Shirai T (1983) Simultaneous determinationof total nitrogen and total phosphorus in water using peroxodi-sulfate oxidation Water Research 17 1721ndash1726 httpsdoiorg1010160043-1354(83)90192-6
EnwrightNGriffithKampOslandM (2016)Barriers to andopportu-nities for landwardmigrationof coastalwetlandswith sea-level riseFrontiers in Ecology and the Environment 14 307ndash3016 httpsdoiorg101002fee1282
FrascoBampGoodeR(1982)DecompositiondynamicsofSpartina alterni-flora and Spartina patensinaNewJerseysaltmarshAmerican Journal of Botany 69402ndash406httpsdoiorg1023072443145
Gallagher J Kibby H amp Skirvin K (1984) Community respi-ration of decomposing plants in Oregon estuarine marshesEstuarine Coastal and Shelf Science 18 421ndash431 httpsdoiorg1010160272-7714(84)90081-7
GambrellRampPatrickW (1978)ChemicalandbiologicalpropertiesofanaerobicsoilsandsedimentsInDHookampMCrawford(Eds)Plant life in anaerobic environments(pp375ndash423)AnnArborMIAnnArborScience
GaoYAbdel-SalamMChenKampWojciechowskiA(2005)Pointre-al-timekinematicpositioningInFSanso(Ed)A window on the future of geodesy vol 128 International Association of Geodesy Symposia (pp77ndash82)BerlinGermanySpringer
Godshalk G amp Wetzel R (1978) Decomposition of aquatic an-giosperms III Zostera marina L and a conceptual model ofdecomposition Aquatic Botany 5 329ndash354 httpsdoiorg1010160304-3770(78)90075-X
GuoXLuXTongSampGuohuaD(2008)Influenceofenvironmentandsubstrate quality on the decompositionofwetlandplant root in theSanjiangPlainNortheastChinaJournal of Environmental Science 20 1445ndash1452httpsdoiorg101016S1001-0742(08)62547-4
HackneyCampde laCruzA (1980) In situdecompositionof rootsandrhizomesoftwotidalmarshplantsEcology 61226ndash231httpsdoiorg1023071935178
HalupaPampHowesB(1995)EffectsoftidallymediatedlittermoisturecontentondecompositionofSpartina alterniflora and S patens Marine Biology 123379ndash391httpsdoiorg101007BF00353629
HarteJampShawR (1995)Shiftingdominancewithinamontanevege-tationcommunitymdashResultsofaclimatewarmingexperimentScience 267876ndash880httpsdoiorg101126science2675199876
HemmingaMAKokCJampdeMunckW (1988)DecompositionofSpartina anglicarootsandrhizomesinasaltmarshoftheWesterscheldeEstuary Marine Ecology Progress Series 48 175ndash184 httpsdoiorg103354meps048175
HerbertERBoonPBurginAJNeubauerSCFranklinRBArdonM hellip Gell P (2015) A global perspective on wetland salinizationEcologicalconsequencesofagrowingthreattofreshwaterwetlandsEcosphere 61ndash43httpdxdoiorg101890ES14-005341
HesterMMendelssohnIampMcKeeK (2001)Speciesandpopulationvariation to salinity stress in Panicum hemitomon Spartina patens and Spartina alternifloraMorphologicalandphysiologicalconstraints
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
OdumW E (1988) Comparative ecology of tidal freshwater and saltmarshes Annual Review of Ecology Evolution and Systematics 19147ndash176httpsdoiorg101146annureves19110188001051
OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
OlsenSRampSommersLE(1982)SoilphosphorusInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and micro-biological properties (pp403ndash430)MadisonWISoilScienceSocietyofAmerica
OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
RDevelopmentCoreTeam(2013)R A language and environment for statis-tical computingViennaAustriaRFoundationforStatisticalComputingRetrievedfromhttpwwwR-projectorgISBN3-900051-07-0
ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
RybczykJGarsonGampDayJJr (1996)Nutrientenrichmentandde-composition in wetland ecosystems Models analyses and effectsCurrent Topics in Wetland Biogeochemistry 2 52ndash72
SAS Institute Inc (2011)Base SASreg 93 procedures guideCaryNCSASInstituteInc
Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
668emsp |emsp emspenspJournal of Ecology STAGG eT Al
Environmental and Experimental Botany 46 277ndash297 httpsdoiorg101016S0098-8472(01)00100-9
HodsonRChrsitianRampMaccubbinA (1984)Lignocelluloseandlig-nin in the saltmarshgrassSpartina alterniflora Initial concentrationsand short-term post-depositional changes in detritalmatterMarine Biology 81 1ndash7
HopfenspergerKBurginASchoepferVampHeltonA (2014) Impactsofsaltwater incursiononplantcommunitiesanaerobicmicrobialme-tabolismandresultingrelationshipsinarestoredfreshwaterwetlandEcosystems 17792ndash807httpsdoiorg101007s10021-014-9760-x
JanousekCBuffingtonKGuntenspergenGThorneKDuggerBampTakekawaJ (2017) Inundationvegetation and sediment effects onlitterdecompositioninpacificcoasttidalmarshesEcosystemshttpsdoiorg101007s10021-017-0111-6
JobbagyEampJacksonR(2000)TheverticaldistributionofsoilorganiccarbonanditsrelationtoclimateandvegetationEcological Applications 10423ndash436 httpsdoiorg1018901051-0761(2000)010[0423TVDOSO]2 0CO2
Kardol P Campany C Souza L Norby R J Weltzin J F ClassenA T (2010) Climate change effects on plant biomass alter domi-nance patterns and community evenness in an experimental old-field ecosystem Global Change Biology 16 2676ndash2687 httpsdoiorg101111j1365-2486201002162x
KeeneyDampNelsonD (1982)Nitrogenndash Inorganic forms InAPageRMillerampDKeeney (Eds)Methods of soil analysis Part 2 chemical and microbiological properties(pp643ndash649)MadisonWISoilScienceSocietyofAmerica
KirwanMLLangleyJAGuntenspergenGRampMegonigalJP(2013)Theimpactofsea-levelriseonorganicmatterdecayratesinChesapeakeBaybrackishtidalmarshesBiogeosciences 101869ndash1876
KraussKDubersteinJDoyleTConnerWDayR InabinetteLampWhitbeckJ (2009)Siteconditionstructureandgrowthofbaldcy-pressalongtidalnon-tidalsalinitygradientsWetlands 29505ndash519httpsdoiorg10167208-771
Laursen K (2004) The effects of nutrient enrichment on the decomposi-tion of belowground organic matter in a Sagittaria lancifoliadominated oligohaline marshMSthesisLouisianaStateUniversityBatonRougeLouisiana
LeadleyPNiklausPStockerRampKornerC(1999)AfieldstudyoftheeffectsofelevatedCO2onplantbiomassandcommunitystructureinacalcareous grassland Oecologia 11839ndash49httpsdoiorg101007s004420050701
LoomisMampCraftC(2012)Carbonsequestrationandnutrient(nitrogenphosphorus)accumulation in riverdominatedtidalmarshesGeorgiaUSASoil Science Society of America Journal 74 1028ndash1036
LopesMMartinsPRicardoFRodriguesAampQuintinoV (2011)In situ experimental decomposition studies in estuaries A com-parison of Phragmites australis and Fucus vesiculosus Estuarine Coastal and Shelf Science 92 573ndash580 httpsdoiorg101016 jecss201102014
MaccubbinA amp Hodson R (1980)Mineralization of detrital lignocel-lulosesby saltmarsh sedimentmicrofloraApplied and Environmental Microbiology 40735ndash740
MaltbyE (1988)Useofcottonstripassay inwetlandanduplandenvi-ronmentsmdashAn international perspective In A Harrison P Latter ampDWalton (Eds)Cotton strip assay An index of decomposition in soils (pp 140ndash154) Grange-Over-Sands Cumbria Institute of TerrestrialEcology
MarinucciACHobbieJEampHelfrichJVK(1983)Effectsoflitterni-trogenondecompositionandmicrobialbiomassinSpartina alterniflora Microbial Ecology 927ndash40httpsdoiorg101007BF02011578
McCleod E Chmura G Bouillon S Salm R BjorkM Duarte C hellipSillimanB (2011)Ablueprint forbluecarbonTowardan improvedunderstandingoftheroleofvegetatedcoastalhabitatsinsequestering
CO2 Frontiers in Ecology and the Environment 9552ndash560httpsdoiorg101890110004
McKeeKampMendelssohnI(1989)Responseofafreshwatermarshplantcommunity to increased salinity and increased water level Aquatic Botany 34301ndash316httpsdoiorg1010160304-3770(89)90074-0
McKeeKampSenecaE(1982)Theinfluenceofmorphologyindetermin-ing the decomposition of two salt marsh macrophytes Estuaries 5 302ndash309httpsdoiorg1023071351753
MelilloJMAberJampMuratoreJ(1982)Nitrogenandlignincontrolofhardwood leaf litter decompositiondynamicsEcology 63 621ndash626 httpsdoiorg1023071936780
Melillo JM Naiman R J Aber J D amp Eshleman K N (1983) Theinfluence of substrate quality and stream size on wood decompo-sition dynamics Oecologia 58 281ndash285 httpsdoiorg101007BF00385224
MelilloJMNaimanRAberJampLinkinsA(1984)Factorscontrollingmass lossandnitrogendynamicsofplant litterdecaying innorthernstreamsBulletin of Marine Science 35341ndash356
MendelssohnI(1979)Theinfluenceofnitrogenlevelformandapplica-tionmethodonthegrowthresponseofSpartina alterniflora inNorthCarolina Estuaries 2106ndash112httpsdoiorg1023071351634
MendelssohnISorrellBBrixHSchierupHLorenzenBampMaltbyE(1999)Controlsonsoilcellulosedecompositionalongasalinitygra-dientinaPhragmites australiswetlandinDenmarkAquatic Botany 64 381ndash398httpsdoiorg101016S0304-3770(99)00065-0
MoranMampHodsonR(1989)Bacterialsecondaryproductiononvascu-larplantdetritusRelationshipstodetrituscompositionanddegrada-tionrateApplied and Environmental Microbiology 552178ndash2189
MorrisJ(1980)ThenitrogenuptakekineticsofSpartina alterniflora in cul-tureEcology 611114ndash1121httpsdoiorg1023071936831
MorriseyEBerrierDNeubauerSampFranklinR(2014)Usingmicro-bial communities and extracellular enzymes to link soil organicmat-tercharacteristicstogreenhousegasproductioninatidalfreshwaterwetland Biogeochemistry 117 473ndash490 httpsdoiorg101007s10533-013-9894-5
NelsonDWampSommersLE(1982)TotalcarbonorganiccarbonandorganicmatterInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and microbiological properties (pp539ndash577)MadisonWISoilScienceSocietyofAmerica
Neubauer S (2013) Ecosystem responses of a tidal freshwater marshexperiencing saltwater intrusion and altered hydrology Estuaries and Coasts 36 491ndash507 httpsdoiorg101007s12237-011- 9455-x
NeubauerSFranklinRampBerrierD(2013)Saltwaterintrusionintotidalfreshwatermarshes alters the biogeochemical processing of organiccarbon Biogeosciences 10 8171ndash8183 httpsdoiorg105194bg-10-8171-2013
NeubauerSGivlerKValentineSampMegonigalJ(2005)Seasonalpat-ternsandplant-mediatedcontrolsofsubsurfacewetlandbiogeochem-istryEcology 863334ndash3344httpsdoiorg10189004-1951
NewellSArsuffiTampPalmL(1996)MistingandnitrogenfertilizationofshootsofasaltmarshgrassEffectsuponfungaldecayofleafbladesOecologia 108495ndash502httpsdoiorg101007BF00333726
NoeGKraussK LockabyBConnerWHHuppCR (2013)Theeffect of increasing salinity and forest mortality on soil nitrogenand phosphorus mineralization in tidal freshwater forested wet-lands Biogeochemistry 114 225ndash244 httpsdoiorg101007s10533-012-9805-1
OdumW E (1988) Comparative ecology of tidal freshwater and saltmarshes Annual Review of Ecology Evolution and Systematics 19147ndash176httpsdoiorg101146annureves19110188001051
OliverHLotterAampLemckeG(2001)LossonignitionasamethodforestimatingorganicandcarbonatecontentinsedimentsReproducibilityandcomparabilityofresultsJournal of Paleolimnology 25 101ndash110
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
OlsenSRampSommersLE(1982)SoilphosphorusInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and micro-biological properties (pp403ndash430)MadisonWISoilScienceSocietyofAmerica
OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
RDevelopmentCoreTeam(2013)R A language and environment for statis-tical computingViennaAustriaRFoundationforStatisticalComputingRetrievedfromhttpwwwR-projectorgISBN3-900051-07-0
ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
RybczykJGarsonGampDayJJr (1996)Nutrientenrichmentandde-composition in wetland ecosystems Models analyses and effectsCurrent Topics in Wetland Biogeochemistry 2 52ndash72
SAS Institute Inc (2011)Base SASreg 93 procedures guideCaryNCSASInstituteInc
Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
emspensp emsp | emsp669Journal of EcologySTAGG eT Al
OlsenSRampSommersLE(1982)SoilphosphorusInAPageRMillerampDKeeney(Eds)Methods of soil analysis Part 2 chemical and micro-biological properties (pp403ndash430)MadisonWISoilScienceSocietyofAmerica
OsborneTInglettPampReddyK(2007)Theuseofsenescentplantbio-mass to investigate relationships between potential particulate anddissolvedorganicmatter inawetlandecosystemAquatic Botany 86 53ndash61httpsdoiorg101016jaquabot200609002
OslandM J Enwright NM Day R H Gabler CA Stagg C LampGraceJB (2016)Beyond just sea-level riseConsideringmac-roclimatic driverswithin coastalwetlandvulnerability assessmentsto climate change Global Change Biology 22 1ndash11 httpsdoiorg101111gcb13084
OslandM EnwrightNampStaggC (2014) Freshwater availability andcoastalwetlandfoundationspeciesEcologicaltransitionsalongarainfallgradientEcology 952789ndash2802httpsdoiorg10189013-12691
Owensby C Coyne PHam JAuen L ampKnappA (1993) Biomassproduction in a tallgrass prairie ecosystem exposed to ambientand elevated CO2 Ecological Applications 3 644ndash653 httpsdoiorg1023071942097
PoideNeiffANeiffJampCascoS(2006)LeaflitterdecompositioninthreewetlandtypesoftheParanaacuteRiverFloodplainWetlands 26 558ndash566 httpsdoiorg1016720277-5212(2006)26[558LLDITW]20 CO2
Ponnamperuma F (1984) Effects of flooding on soils In T Kozlowski(Ed) Flooding and plant growth (pp 10ndash45)Orlando FLAcademicPressInc
RDevelopmentCoreTeam(2013)R A language and environment for statis-tical computingViennaAustriaRFoundationforStatisticalComputingRetrievedfromhttpwwwR-projectorgISBN3-900051-07-0
ReddyKampPatrickW(1975)Effectofalternateaerobicandanaerobicconditionson redoxpotentialorganicmatterdecompositionandni-trogenlossinafloodedsoilSoil Biolology and Biochemistry 787ndash94httpsdoiorg1010160038-0717(75)90004-8
ReedD(1995)Theresponseofcoastalmarshestosea-levelriseSurvivalor submergence Earth Surface Processed and Landforms 20 39ndash48httpsdoiorg101002(ISSN)1096-9837
Reice S amp Stiven A (1983) Environmental patchiness litter decom-position and associated faunal patterns in a Spartina alterniflora marsh Estuarine Coastal and Shelf Science 16 559ndash571 httpsdoiorg1010160272-7714(83)90086-0
RhodesJ (1996)Electricalconductivityandtotaldissolvedsolids InDSparks(Ed)Methods of soil analysis Chemical methods(pp417ndash437)MadisonWISoilScienceSocietyofAmerica
RybczykJGarsonGampDayJJr (1996)Nutrientenrichmentandde-composition in wetland ecosystems Models analyses and effectsCurrent Topics in Wetland Biogeochemistry 2 52ndash72
SAS Institute Inc (2011)Base SASreg 93 procedures guideCaryNCSASInstituteInc
Saunders CMegonigal JampReynolds J F (2006) Comparison of be-lowground biomass in C3-andC4-dominatedmixedcommunitiesinaChesapeakeBaybrackishmarshPlant and Soil 280305ndash322httpsdoiorg101007s11104-005-3275-3
ScartonFDayJampRismondoA(2002)Primaryproductionanddecom-positionofSarcocornia fruticosa(L)ScottandPhragmites australis Trin ExSteudel in thePoDelta ItalyEstuaries 23 325ndash336httpsdoiorg101007BF02695977
Schipper LampReddyK (1995) In situ determinationof detrital break-downinwetlandsoil-floodwaterprofileSoil Science Society of America Journal 59565ndash568httpsdoiorg102136sssaj199503615995005900020042x
SchubauerJPampHopkinsonCS(1984)Above-andbelowgroundemer-gentmacrophyteproductionandturnoverinacoastalmarshecosys-temGeorgiaLimnology and Oceanography 291052ndash1065httpsdoiorg104319lo19842951052
SharpePampBaldwinA(2012)Tidalmarshplantcommunityresponsetosea-levelriseAmesocosmstudyAquatic Botany 10134ndash40httpsdoiorg101016jaquabot201203015
SlocumMRobertsJampMendelssohnI (2009)Artistcanvasasanewstandard for thecotton-stripassayJournal of Plant Nutrition and Soil Science 17271ndash74httpsdoiorg101002jpln200800179
SmallCampNichollsR (2003)Aglobalanalysisofhumansettlement incoastalzonesJournal of Coastal Research 19584ndash599
StaggCLBaustianMMPerryCLCarruthersTJBampHallCT(2017)Organicmatterdecompositionacrossacoastalwetlandland-scape in LouisianaUSA (2014-2015)USGeological SurveyDataReleaseRetrievedfromhttpsdoiorg105066F7639MVK
Stagg C L Schoolmaster D R Krauss KW Cormier N amp ConnerWH (2017)Causalmechanismsof soil organicmatterdecomposi-tionDeconstructingsalinityandfloodingimpactsincoastalwetlandsEcology 982003ndash2018httpsdoiorg101002ecy1890
StaggCLSchoolmasterDRPiazzaSCSneddenGSteyerGDFischenich C J amp McComas R W (2017) A landscape-scale as-sessment of above- and belowground primary production in coastalwetlands Implications for climate change-induced communityshifts Estuaries and Coasts 40 856ndash879 httpsdoiorg101007s12237-016-0177-y
SternbergMBrownVMastersGampClarkeI(1999)PlantcommunitydynamicsinacalcareousgrasslandunderclimatechangemanipulationsPlant Ecolology 14329ndash37httpsdoiorg101023A1009812024996
StewartCEPaustianKConantRTPlanteAFampSixJ(2007)SoilcarbonsaturationConceptevidenceandevaluationBiogeochemistry 8619ndash31httpsdoiorg101007s10533-007-9140-0
Sutton-GrierAKellerJKochRGilmourCMegonigalJP(2011)Electrondonorsandacceptorsinfluenceanaerobicsoilorganicmat-termineralizationintidalmarshesSoil Biology and Biogeochemistry 431576ndash1583httpsdoiorg101016jsoilbio201104008
TaylorB ParkinsonDampParsonsW (1989)Nitrogenand lignin con-tentaspredictorsoflitterdecayratesAmicrocosmtestEcology 70 97ndash104httpsdoiorg1023071938416
ThomasGW(1996)SoilpHandsoilacidityInDSparks(Ed)Methods of soil analysis Part 3 Chemical methods (pp 475ndash490) Soil ScienceSocietyofAmericaBookSeriesNo5MadisonWISoilScienceSocietyofAmerica
Valiela ITeal JAllen SVan Etten R GoehringerD ampVolkman S(1985) Decomposition in salt marsh ecosystems The phases andmajorfactorsaffectingdisappearanceofabove-groundorganicmatterJournal of Experimental Marine Biology and Ecology 8929ndash54httpsdoiorg1010160022-0981(85)90080-2
ValielaIWilsonJBuchsbaumRRietsmaCBryantDForemanKampTealJ(1984)ImportanceofchemicalcompositionofsaltmarshlitterondecayratesandfeedingbydetritivoresBulletin of Marine Science 35261ndash269
VanSoestPampWineR(1968)Determinationofligninandcelluloseinacid-detergent fiberwithpermanganate Journal of the Association of Official Analytical Chemists 51 780ndash785
Vasilas L amp Vasilas B (2013) Hydric soil identification techniquesIn J Anderson amp C Davis (Eds) Wetland techniques Vol 1 Foundations (pp 227ndash272) Berlin Germany Springer httpsdoiorg101007978-94-007-6860-4
VisserJDuke-SylvesterSCarterJampBroussardWIII(2013)Acom-putermodeltoforecastwetlandvegetationchangesresultingfromres-torationandprotectionincoastalLouisianaJournal of Coastal Research 6751ndash59httpsdoiorg102112SI_67_4
VisserJSasserCChabreckRampLinscombeR(2002)TheimpactofaseveredroughtonthevegetationofasubtropicalestuaryEstuaries 25 1184ndash1195httpsdoiorg101007BF02692215
Warren R amp NieringW (1993)Vegetation change on northeast tidalmarsh Interactionofsea-level riseandmarshaccretionEcology 74 96ndash103httpsdoiorg1023071939504
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901
670emsp |emsp emspenspJournal of Ecology STAGG eT Al
WebsterJRampBenfieldEF(1986)Vascularplantbreakdowninfresh-waterecosystemsAnnual Review of Ecology Evolution and Systematics 17567ndash594httpsdoiorg101146annureves17110186003031
WeiderRampLangG(1982)AcritiqueoftheanalyticalmethodsusedinexaminingdecompositiondataobtainedfromlitterbagsEcology 63 1636ndash1642httpsdoiorg1023071940104
WelschMampYavittJ(2003)EarlystagesofdecayinLythrum salicariaLand Typha latifoliaL inastanding-deadpositionAquatic Botany 75 45ndash57httpsdoiorg101016S0304-3770(02)00164-X
WestonNDixonRampJoyeS(2006)Ramificationsofincreasedsalin-ity in tidal freshwater sediments Geochemistry andmicrobial path-waysoforganicmattermineralizationJournal of Geophysical Research Biogeosciencs 1111ndash14httpsdoiorg1010292005JG000071
WestonNNeubauerSCVelinskyDJampVileMA(2014)Neteco-system carbon exchange and the greenhouse gas balance of tidalmarshesalonganestuarysalinitygradientBiogeochemistry 120 163ndash189httpsdoiorg101007s10533-014-9989-7
WestonNVileMNeubauerSampVelinskyD(2011)Acceleratedmi-crobialorganicmattermineralizationfollowingsalt-waterintrusionintotidal freshwatermarsh soilsBiogeochemistry 102 135ndash151httpsdoiorg101007s10533-010-9427-4
White D amp Trapani J (1982) Factors influencing disappearance ofSpartina alterniflora fromlitterbagsEcology 63242ndash245httpsdoiorg1023071937047
Wilson J (1985) Decomposition of [14C]lignocelluloses of Spartina al-terniflora and a comparison with field experiments Applied and Environmental Microbiology 49478ndash484
Wilson J Buchsbaum RValiela I amp SwainT (1986)Decompositionin salt marsh ecosystems Phenolic dynamics during decay of litter
ofSpartina alterniflora Marine Ecology - Progress Series 29 177ndash187 httpsdoiorg103354meps029177
WindhamL (2001)Comparisonofbiomassproductionanddecomposi-tionbetweenPhragmites australis (commonreed)andSpartina patens (salthaygrass)inbrackishtidalmarshesofNewJerseyUSAWetlands 21 179ndash188 httpsdoiorg1016720277-5212(2001)021[0179COBPAD]20CO2
WoltersVSilverWBignellDColemanPvanderPuttenWdeRuiterPhellipvanVeenJ(2000)Effectsofglobalchangesonabove-andbelow-groundbiodiversityinterrestrialecosystemsImplicationsforecosystemfunctioningBioScience 501089ndash1098httpsdoiorg1016410006-3568(2000)050[1089EOGCOA]20CO2
SUPPORTING INFORMATION
Additional Supporting Information may be found online in the supportinginformationtabforthisarticle
How to cite this articleStaggCLBaustianMMPerryCLCarruthersTJBHallCTDirectandindirectcontrolsonorganicmatterdecompositioninfourcoastalwetlandcommunitiesalongalandscapesalinitygradientJ Ecol 2018106655ndash670 httpsdoiorg1011111365-274512901