Elevated CO2 enhances short-term recovery after extreme drought and heat in a temperate grassland.

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Elevated CO2 enhances short-term recovery after

extreme drought and heat in a temperate grassland.

Catherine Picon-Cochard, J. Roy, D. Landais, Marie-Lise Benot, C. Piel, M.

Defossez, C. Escape, S. Devidal, O. Ravel, M. Bahn, et al.

To cite this version:

Catherine Picon-Cochard, J. Roy, D. Landais, Marie-Lise Benot, C. Piel, et al.. Elevated CO2 enhances

short-term recovery after extreme drought and heat in a temperate grassland.. Climate Change and

Food Security Conference, May 2014, Madrid, Spain. 2014. �hal-02795730�

Before After 0 50 100 150 200 250 380 C BNPP 380E: 39.23 520 C 520 E 380 E 01/0 5 01/0 6 01/0 7 01/0 8 01/0 9 01/1 0 01/1 1 0 5 10 15 20 UREP Grassland Ecosystem Research Clermont-Ferrand

Elevated CO

₂

enhances short-term recovery after

extreme drought and heat in a temperate grassland

Picon-Cochard C1_{, Roy J}2_{, Landais D}2_{, Benot M-L}1,3_{, Piel C}2_{, Defossez M}2_{, Escape C}2_{, Devidal S}2_{, Ravel O}2_{, Bahn M}4_,

Volaire F5_{, Augusti A}1,6_{, Soussana J-F}1

1: Grassland Ecosystem Research Unit, UR874, INRA Clermont-Ferrand, France; 2: Ecotron Montpellier, CNRS, France; 3: Biogeco, University of Bordeaux, France; 4: Institute of Ecology, University of Innsbruck, Austria; 5: Centre d’Ecologie Fonctionelle et Evolutive, CNRS, France; 6: Institute of Agro-environmental and Forest Biology, CNR, Porano, Italy; Email: catherine.cochard@clermont.inra.fr

Under warmer and drier climatic conditions, increase of atmospheric CO₂ concentration is expected to limit the negative effects of stress on grassland production. The capacity to recover after drought could also be favored by elevated CO₂, as it may improve plant growth through its primary effects on both leaf photosynthesis and stomatal conductance.

The aim of this study was to evaluate a possible mitigation effect of elevated CO₂on canopy C and water fluxes, and its consequences on forage production and quality, during and after an extreme event (soil drought x heat).

METHODS

48 grassland monoliths (1m x 1m x 0.6 m depth, upland site: Auvergne, France) in 12 experimental units.

Year 1: monoliths exposed to air temperature (T) and precipitation (P) expected for 2040-2060: 2.3 C warming combined with 10% reduction of P by comparison to average climatic conditions

Year 2: 6 of the 12 units exposed to elevated CO2, i.e. 520 µmol mol-1, compared with ambient CO2, i.e. 380 µmol mol-1.

• In Summer, P reduction from end of June during 1 month, then no watering combined with a heat wave (+3 C) during 17 days, and finally progressive rehydration until fall. • Treatments: 380 C and 520 C: without heat wave and drought, 380 E and 520 E: with heat

weave and drought

C and water fluxes: gross primary production (GPP), evapotranspiration (ET) and soil water content (SWC, 0-60cm) were continuously measured. Water-use efficiency was calculated as WUE = GPP / ET.

Above and below-ground (ingrowth-core method, picture) biomasses, forage quality (N, NDF: total cell wall) were measured before stress and after rehydration at cut date.

RESULTS

INTRODUCTION

Under future climatic conditions (warmer and drier) forecasted for 2040-2060

 Elevated CO2mitigated the negative effect of drought x heat by increasing GPP and WUE, and promoted recovery of

this permanent grassland

 These changes led to higher root biomass with no effect on above-ground production  Forage quality was affected: more digestible forage but containing less N

 This study confirmed the short-term recovery capacity of permanent grassland after severe drought and heat

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) for their helpful contribution to the realization of this project.

Before extreme

Heat wave x drought

After

Root ingrowth-core

Inside an experimental unit

Higher GPP and WUE

under elevated CO₂

Before stress due to

slightly higher SWC (+5%)
During stress for similar SWC and evapotranspiration
After rehydration at similar evapotranspiration but lower SWC

Soil water content (SWC, %) Gross primary production (GPP, gCO2m-2d-1)

Water-use efficiency (WUE, mgCO2g-1H2O)

Stress After Before

Under elevated CO₂

Before stress: above and below-ground biomasses were unchanged, and lower N and NDF

After stress: higher root biomass and lower N and NDF Before After 0 50 100 150 200 250

Green biomass (g DM m-2_{) Root biomass (g DM m}-2₎

* NS Before After 40 45 50 55 60 Before After 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 N (%) NDF (%) * a _ab bc c * _a b b 0 10 20 30 0 2 4 6 8 10 12 Before 0 10 20 30 380 C 380 E 520 C 520 E Stress 0 10 20 30 40 After