VALIDATE (ANR funded project, 2011-2012)

Impact of extreme climate events (drought and heat wave) on grasslands interaction with CO2 increase.
Coordination INRA at Clermont-Ferrand (with CEFE-CNRS, Austria, Germany).
Consequences on:

  • biogeochemical cycles (carbon storage, water and nitrogen balance...);
  • biodiversity (soil and vegetation);
  • quantity and quality of green biomass.

Montpellier Ecotron

The results of this first experiment have been presented at the Climate Extremes and Biogeochemical Cycles Conference (Innsbrück, 2-5 April 2013) and at the European Geosciences Union General Assembly (Vienna, 7-12 April 2013)

Abstract: Summer extreme climatic event in the future: impact on the net CO2 and water fluxes of an upland grassland and buffering impact of elevated atmospheric CO2.

Jacques Roy1, Damien Landais1, Clément Piel1, Marc Defossez1, Christophe Escape1, Sébastien Devidal1, Philippe Didier1, Olivier Ravel1, Michael Bahn2, Florence Volaire3, Angela Augusti4  Jean-François Soussana4, Catherine Picon-Cochard4

1) European Ecotron of Montpellier CNRS France, 2) Institute of Ecology University of Innsbruck Austria, 3) CEFE CNRS, INRA  Montpellier France, 4) UREP INRA Clermont-Ferrand France

Extreme climatic events are expected to be more frequent and intense in a few decades, but they will also occur in a climatic context different from the current one.  In the Montpellier Ecotron, we studied the response of intact grassland monoliths (1m², 60 cm deep) sampled in an upland grassland of the French Massif Central. The first year the grasslands were acclimated to the average climatic conditions of the years around 2050 (+ 4 °C and – 56 mm for summer precipitations). The second year, the same climate was maintained but in half of the experimental units we imposed a summer drought and heat wave (50 % reduction of precipitations for a month and then 100 % precipitation reduction combined with a 3,4 °C increase in temperature for two weeks). A CO2 treatment (520 vs. 380 µmol/mol) was crossed with the climatic treatment.
Net CO2 fluxes were measured continuously during the second year of the experiment. The extreme climatic event induced a total senescence of the canopy whatever the CO2 treatment. The interactive effect of elevated CO2 with the drought treatment was significant at the onset of the drought and particularly large in the fall after the recovery period, with a net photosynthesis twice as high in the (extreme climate+ CO2) treatment compared to the control. Integrated over the year, elevated CO2 totally buffered the impact of the extreme climatic event on net CO2 exchanges. These results are discussed together with the evapotranspiration and soil humidity data.