Seasonal change effects on photosynthesis, nitrogen metabolism

and soil nitrogen in competing invasive Phalaris arundinacea and

native Carex stricta

Elizabeth Waring and A. Scott Holaday

Texas Tech University

Why study physiology in invasive species?

GrowthReproduct

ion

Metabolic Adaptations

Soil NitrogenSeasonal Changes

Performance

Physiological

Processes

Environment

Wetlands and Invasion• Wetlands are particularly likely to be

invaded1 – Sinks in hydrological systems– Seeds and plant parts are easily

dispersed by water• Nitrogen sinks

– Increasing from anthropogenic changes• Phalaris arundinacea/Carex stricta

model1 Zedler and Kercher 2004

Phalaris arundinacea L.• “Reed

Canarygrass”• Few native

populations in North America

• Mostly hybrid of native European and Asian populations

• Increased biomass with increased nitrogen

Carex stricta Lam• “Tussock Sedge”• Native east of

Great Plains• Biodiversity

Research Questions• (1) Do the species differ with respect to

nitrogen assimilation that affects photosynthetic processes?

• (2) Is there a relationship between seasonal changes in physiological processes and available soil nitrogen?

Nitrogen Assimilation

NO2- NH4

+

Building Amino Acids

NO3-

Soil Plant

NR NiR

NH4+

Leaf Nitrogen, Protein Content and Photosynthesis• First step of

Calvin-Benson Cycle catalyzed by Rubisco

• Strong relationship • Link carbon and

nitrogen metabolism

• Leaf N – mg/g leaf tissue – CE Elantech

• Protein by Bradford Assay1

Wright et al. 2004

1 Bradford 1976

Photosynthesis

Ci (ppm)

Soil Probes• Cation and anion• Trap moving

nitrogen• In soil for 3 weeks• 4 blocks of 4 pairs

per site• Analyzed in at

Western Ag labs in ND

• Data were collected seasonally in 2012

• Leaf N from 2011• Tissue samples

collected in May, July, October

Site 1 (“Phalaris site”)• Phalaris dominated • Some Carex species

mixed• Low Biodiversity

Site 1 (“Phalaris site”)• Phalaris dominated • Some Carex species

mixed• Low Biodiversity

Site 1 (“Phalaris site”)• Phalaris dominated • Some Carex species

mixed• Low Biodiversity

Site 2 (“Carex site”)• Some Phalaris on

East side• High Biodiversity

Site 2 (“Carex site”)• Some Phalaris on East

side• High Biodiversity

Site 2 (“Carex site”)• Some Phalaris on East

side• High Biodiversity

SLA

Statistical Analysis• Seasons to Julian date• Mixed Effects Linear Regression

Model in R• Nested by individual (repeated

measurements)• Followed by ANOVA

Mixed effects model nested by individual (n=4)spp p<0.05 and dateXspp p <0.05

Mixed effects model nested by individual (n=4)spp p<0.05 and dateXspp p <0.05

2011 dataMixed effects model nested by individual (n=4)spp p<0.05 and date p <0.05

Mixed effects model nested by individual (n=6)Spp, date, and site p<0.05 and dateXspp p <0.0001 and dateXsppXsite p<0.05

Mixed effects model nested by individual (n=6)spp p<0.005 and date p <0.0001

Mixed effects model nested by individual (n=6)Site p<0.1 and date p <0.0001

Nitrate:Site p<0.005

Ammonium

Site p<0.05Date p<0.005DateXSite p<0.05

Conclusions• (1) Do the species differ with respect to

nitrogen assimilation that affects photosynthetic processes?– Yes. Although mostly in Carex

• (2) Is there a relationship between seasonal changes in physiological processes and available soil nitrogen?– Carex No– Phalaris Possibly. Few traits varied between

sites, but appears Phalaris increased dominance with increased nitrate?

Future Directions• Expand sampling sites• Use proxies

– Leaf N– Soil N– Protein content

• >20 sites sampled in May

Acknowledgements

• Hasitha Guvvala and Yuanhua Wang• Moore-Kucera lab• The Wetland Foundation• Department of Biological Sciences• VPR Office