Romain BARNARD

Romain BARNARD

Chercheur INRA

Projet INCITE

Integrated response of plant, microbial and N Cycling InTEractions to precipitation patterns

Soil microbial communitystructure and activity

Climate change predictions in Europe: less precipitation amounts

more intense and less frequent rain events

Impacts three main aspects of plant-soil interactions, affecting productivity, C budgets and N losses

Stimulation of biogeochemical cycles

Stimulation of nutrient uptake by plants and microorganisms

N and C functions and cycling in the soil

N2OCO2

Stimulation of greenhouse gas emissions

Context

H2O

Plant water and nutrientuptake

H2O

N2OCO2

Soil microbial communitystructure and activity

N and C functions and cycling in the soil

Plant water and nutrientuptake

Impacts on biogeochemical cycles, plant-microbe competition and synchronicity2

2

2

Stability of microbial community vs. stability of biogeochemical functions3

3

Microbial activity, coupling with plant water uptake depth1

1

1

Objectives

Soil matrix↑ spatially disconnected↑ aerobic↓ osmotic potential

Soil microbes↑ spatially isolated↓ general activity↑ survival strategies

Plant↓ photosynthesis rate↓? rhizodeposition

↓ plant-microbial coupling

Drying Rewetting

Soil matrix↑ spatially connected↑ anaerobic↑ osmotic potential

Soil microbes↑ osmo-regulation↑ motility↑ burst of activity

Plant↑ photosynthesis rate ↑? rhizodeposition

↑ plant-microbial coupling

Dry - Wet

C C

Precipitation regimes: Equal total volume but different frequency

Frequent Small volume

0-5 cm

10-15 cm

30-35 cm

Infrequent Large volume

1 Depth

Engelhardt et al. (2018) The ISME Journal

1 Depth

100 200 300 400 500

−26

−25

−24

−23

−22

Root biomass (g m-2

)

d1

3C

in

mic

rob

ial b

iom

ass (‰

)

●

●

Freq. Infreq.

● ●

topmiddlebottom

Frequent treatment:

↑ live root biomass

↑ available C

↑ 13C immobilization

Infrequent treatment:Loss of plant-microbial coupling in top soil layer

Precipitation regime legacy effect on C flux from plant to microbes

100 200 300 400 500

−26

−25

−24

−23

−22

Root biomass (g m-2

)

d1

3C

in

mic

rob

ial b

iom

ass (‰

)

●

●

Freq. Infreq.

● ●

topmiddlebottom

1 Depth

Active Inactive

Depth 12 20

Precipitation legacy ns ns

Depth x Precip. leg. ns ns

% variance explained

Freq InfreqRewetting response shaped bacterial communities

Analysing active and inactive community independently: large amount of variation due to depth

but no effect of precipitation legacy

BACTERIA

FUNGI1400

1450

1500

1550

1600

avg_all[avg_all$activity == "active", ]$SimRec

obs index

●

●

act. inact.

● ●

top

middle

bottom

600

800

1000

1200

1400

fung_avg_all[fung_avg_all$activity == "active", ]$SimRec

fung_avg_a

ll[fu

ng_avg_all$

activity =

= "

active",

]$ob

s

●

●

40 60 80 100 120 140

Spe

cie

s r

ich

ne

ss

Evenness (Simpson reciprocal index)

1 Depth

Across different environmental conditions of the soil profile, the diversity of active

bacteria is unchanged and they are phylogenetically clustered

Overall: No significant effect of precipitation history on bacterial or fungal

diversity, but depth response

Across precipitation treatments:

1400

1450

1500

1550

1600


obs index

●

●

act. inact.

● ●

top

middle

bottom

600

800

1000

1200

1400


fung_avg_a

ll[fu

ng_avg_all$

activity =

= "

active",

]$ob

s

●

●

40 60 80 100 120 140

Spe

cie

s r

ich

ne

ss


1400

1450

1500

1550

1600


obs index

●

●

act. inact.

● ●

top

middle

bottom

600

800

1000

1200

1400


fung_avg_a

ll[fu

ng_avg_all$

activity =

= "

active",

]$ob

s

●

●

40 60 80 100 120 140

Spe

cie

s r

ich

ne

ss


1400

1450

1500

1550

1600


obs index

●

●

act. inact.

● ●

top

middle

bottom

600

800

1000

1200

1400


fung_avg_a

ll[fu

ng_avg_all$

activity =

= "

active",

]$ob

s

●

●

40 60 80 100 120 140

Spe

cie

s r

ich

ne

ss


1 Depth

Frequent Infrequent

Top 0-5cm depth: significant precipitation regime effects on microbial diversity

Precipitation pattern affected not only fungal:bacterial ratio but also their relative activity

1400

1450

1500

1550

1600


obs index

act. inact.

freq.

infreq.

600

800

1000

1200

1400


fung_avg_a

ll[fu

ng_avg_all$

activity =

= "

active",

]$ob

s

20 40 60 80 100 120 140

Spe

cie

s r

ich

ne

ss


BACTERIA

FUNGI

In top soil:

At 0-5 cm depth: bacterial seed bank reflects legacy more than active players.

1 Depth

top bottom

Top orders

Bottom orders

FUNGIdominated by phylum Ascomycota

top bottom

Depth groups are dominated by different classes of Proteobacteria

Top and bottom group contain completely different orders of fungi

BACTERIA

Nutrients and time2

NH4+

Microbial biomass N

N2O

nitrification denitrification

Under less frequent precipitationUnder high N inputs

amoA (archaea)potential nitrification

nirK, nirS, nosZ1, nosZ2potential denitrification

biomassphotosynthesis rate

N uptake

Alternating wetter and drier conditions stimulated nitrification-denitrification sequences

N input increased plant N uptake through increased microbial turnover

(underfreq water)

Engelhardt et al. unpubl. data

NO3-

Nutrients and time2

Infrequent precipitation decreased fungal:bacterial ratio

Potential consequences on soil food web stability, as well as soil C sequestration,

and N retention

Nutrients and time

Frequent water, high NFrequent water, low NInfrequent water, high NInfrequent water, low NBACTERIA

During 29 hours after rewetting:

FUNGI

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−0.08 −0.06 −0.04 −0.02 0.00 0.02 0.04

−0.03

−0.02

−0.01

0.00

0.01

0.02

0.03

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F_10N

F_5N

I_10N

I_5N

Bacteria Fungi

Precipitation legacy 18 36

N legacy 35 10

Time after rewetting ns ns

Precip. leg. x Time ns ns

Stability of the microbial community structure over time, after the large immediate response to rewetting

% variance explained

2

Nutrients and time

Soil greenhouse gas emissions upon rewetting

2

Frequent precipitation pattern enhances soil CO2 emissions

upon rewetting

Contrasts with soil-only studies: contribution of root respiration

CO2

N2O

Nutrients and time

Plant-microbial competition for soil inorganic N

2

Frequent precipitation pattern enhances plant competitiveness for N

after rewetting

Soilfood web stability

• Depth shapes structure of soil microbial community more than precipitation legacy

• Top soil is where precipitation history matters:> shift in fungal vs bacterial dominance > loss of plant microbial coupling under infrequent precipitation

• N cycling is stimulated by dry-wet amplitude

• Soil CO2 emissions upon rewetting are related to both root respiration and soil microbial activity

Impact

Soil C sequestration

Soil N losses

Soil CO2

emissionsNext challenge: predictability

Ecosystem property at stake:

INRA Dijon

Ilonka EngelhardtAmy Welty

WSL (Switzerland)

Arthur GesslerLucía GalianoJosé Carlos Miranda

Lawrence LivermoreNational Lab (USA)

Steve Blazewicz

Uni Zurich (Switzerland)

Pascal Niklaus

Lund University(Sweden)

Annelein Meisner

Thanks

Documents

Romain BARNARD