Effects of summer extreme events on grassland soil CO2 efflux in a context of future climate change

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Effects of summer extreme events on grassland soil CO2

efflux in a context of future climate change

Angela Augusti, D Landais, Marie-Lise Benot, R Hasibeder, M Bahn,

Catherine Roumet, J Roy, Jean-François Soussana, Catherine Cochard

To cite this version:

Angela Augusti, D Landais, Marie-Lise Benot, R Hasibeder, M Bahn, et al.. Effects of summer extreme

events on grassland soil CO2 efflux in a context of future climate change. OpenScienceConference on

Climate Extremes and Biogeochemical Cycles in the Terrestrial Biosphere: Impacts and Feedbacks

Across Scales, 2013, Seefeld, Austria. 1 p., 2013. �hal-02806429�

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The recovery of total soil CO₂efflux is associated to a sustained recovery in root respiration (both in newly formed roots from ingrowth core and from soil core), (Fig. 5). A mild effect of increasing CO2can be observed. .00 5.00 10.00 15.00 20.00 25.00 262 R o o t re sp ir a ti o n , µ m o le s C O 2 g D W -1 se c -1

InGrowth Core roots

Fig. 5 .00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 255 277

Soil core roots

380 C 380 E 520 C 520 E Root respiration

UREP

Grassland Ecosystem

Research

Clermont-Ferrand

Effects of summer extreme events on grassland soil

CO

₂

efflux in a context of future climate change

Augusti A.

1,3

_{, Landais D.}

2

_{, Benot M-L.}

3

_{, Hasibeder R.}

4

_{, Bahn M.}

4

_{, Roumet C.}

5

_{, Roy J.}

2

_{, Soussana J.F.}

3

_,

Picon-Cochard C.

3

1: Institute of Agro-environmental and Forest Biology, CNR, Italy; 2: Ecotron Montpellier, CNRS, France; 3: Grassland Ecosystem Research Unit, UR874, INRA Clermont-Ferrand, France; 4: Institute of Ecology, University of Innsbruck, Austria; 5: Centre d’Ecologie Fonctionelle et Evolutive, CNRS, France; Email:angela.augusti@ibaf.cnr.it& catherine.cochard@clermont.inra.fr

Climate models forecast, for the coming century, not only a gradual warming and drier climate, but an increase

in frequency of extreme events, too.

In grassland ecosystem most of the carbon is stored in the soil. Below-ground processes act as feedback on

atmospheric CO

₂

concentration. Soil CO

₂

efflux derives from two main components, autotrophic respiration

being associated with root and rhizosphere respiration and heterotrophic respiration associated with the

turnover of soil organic matter by microorganisms.

The aim of this study was to evaluate the extreme event effects on soil efflux and on its autotrophic and

heterotrophic components, in a context of future climate change. A possible mitigation effect of increasing CO

₂

on soil CO

₂

efflux and its components was evaluated.

Treatments 2010 CO2 May-Dec 2010 T P 380 C 380 2050 2050 380 E 380 2050 2050 520 C 380 2050 2050 520 E 380 2050 2050 2011 CO2 01 Jan-24 Jun Julian days (1-175) 25 Jun-21 Jul (176-202) 22 Jul-08 Aug (203-220) 09 Aug-Nov (204-334) T P T P T P T P 380 2050 2050 2050 2050 2050 2050 2050 2050 380 2050 2050 2050 2050/2 2050 +3,5°C 0 2050 2050 520 2050 2050 2050 2050 2050 2050 2050 2050 520 2050 2050 2050 2050/2 2050 + 3,5°C 0 2050 2050

METHODS

Forty eight grassland monoliths, coming from an upland site in Auvergne Region, France, were grouped in 12 experimental units.

Since May2010, the 12 units were exposed to air temperature (T) and

precipitation (P) expected for the period 2040-2060 (in table indicated as

2050). This corresponded to an increase of 2.3°C in T and to a decrease of 10% in the P compared to a reference year, 1999.

Since January 2011, 6 out of the 12 units were exposed to a CO2

enrichment of 140 ppm more than ambient.

During summer 2011 a heat wave and drought stress were applied.

RESULTS

INTRODUCTION

Summer drought and heat wave stress caused a decrease in soil respiration even if the kinetics differ between total and heterotrophic components. They caused a sustained decrease in root growth and in canopy photosynthesis (see talk of Jacques Roy).

The increasing CO2had a mitigation effect of the extreme on root growth rate and on root respiration, but not on soil CO2efflux.

Eu ropean Proje ct, FP7 Eu ropean Proje ct, FP7

CONCLUSIONS

Angela Augusti and Benot Marie-Lise’s post docs were financed by INRA through scientific package.

We would like to thank the group members of UREP-INRA (O. Darsonville, L. Thiery) and of Ecotron (O. Ravel, C. Escape, C. Piel, S. Devidal) for their helpful contribution to the realization of this project.

The reduction in total soil CO₂efflux is well described by the reduction in soil moisture (Fig. 3a and b).

R² = 0.4156 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 To ta l S o il C O 2 E fl lu x , µ m o l m -2 s -1 380 ppm Extremes R² = 0.4873 0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 To ta l S o il C O 2 E ff lu c, µ m o l m -2 s -1

Soil Moisture at 7cm depth, %

520 ppm Extremes Fig. 3 .000 .500 1.000 1.500 2.000 2.500 3.000 3.500 95 105 115 125 135 145 155 165 175 185 195 205 215 225 235 245 255 265 275 S o il C O2 E ff lu x, n m o l m2 -2 s -1 Julian Days Total Soil Respiration

380 ppm Control 380 ppm Extremes 520 ppm Control 520 ppm Extremes Fig. 1 .000 .200 .400 .600 .800 1.000 1.200 1.400 95 105 115 125 135 145 155 165 175 185 195 205 215 225 235 245 255 265 275 S o il C O2 E ff lu x, n m o le m 2 -2 s -1 Julian Days

Heterotrophic Soil Respiration _{380 ppm Control} 380 ppm Extremes 520 ppm Control 520 ppm Extremes

Fig. 2

Total efflux (Fig.1) is strongly reduced during the extreme event treatments both at ambient and at

elevated CO₂. The reduction is mainly due to the

autotrophic component since the treatments had a milder effect on heterotrophic respiration (Fig.2). Total respiration shows a faster recovery compared to heterotrophic respiration. -0.500 0.000 0.500 1.000 1.500 2.000 2.500 3.000 95 150 205 260 315 R o o t G ro w th r ta e , g D W m -2 d

Root Growth Rate 380 C

380 E 520 C 520 E

The reduction in soil CO₂efflux, induced by the extreme event, is associated to a decrease in root growth rate (Fig. 4a) and to an increase of RDMC (Fig.4b). 0.050 0.100 0.150 0.200 0.250 0.300 0.350 95 150 205 260 315 R D M C Julian Days Root Dry Matter Content Fig. 4 -5 0 5 10 15 20 25 30 35 150 175 200 225 250 275 300 325 350 R o o t lo ss , % Julian Days Root Decomposition 380 ppm Control 380 ppm Extremes 520 ppm Control 520 ppm Extremes Fig. 6

Recovery of root decomposition followed the slower recovery of heterotrophic soil efflux (Fig.6).

a

b