• Reduce text

    Reduce text
  • Restore text size

    Restore text size
  • Increase the text

    Increase the text
  • Print

    Print
View of the inside of an Ecotron macrocosm containing 4 blocks of grassland. © INRA, C. Picon-Cochard

Grasslands recover more easily from heatwaves and droughts when atmospheric CO2 levels are high

Extreme climatic events such as heatwaves and droughts may affect the ability of terrestrial ecosystems to sequester carbon. Recently, INRA and CNRS researchers carried out a large-scale experiment exploring this topic at the Ecotron facility in Montpellier. Using samples of permanent upland grassland, they made an unexpected discovery: elevated levels of atmospheric carbon dioxide help grasslands recover from extreme climatic events and limit the negative impacts of water stress. Published online in an early edition of PNAS, this work underscores the importance of fully examining ecosystem interactions when studying climate change.

Updated on 06/08/2017
Published on 05/23/2016

Experimental blocks of upland grassland being excavated in the Auvergne region of France. © Hubert Raguet
Experimental blocks of upland grassland being excavated in the Auvergne region of France. © Hubert Raguet
Between now and the end of the century, France will experience an increase in the number and severity of extreme climatic events, such as heat waves and droughts, as a result of climate change. These events will negatively impact ecosystems and especially drought-sensitive grasslands, which are important resources for France’s dairy and meat cattle. For instance, soil quality may decline because carbon-rich organic matter may be lost.

However, ironically, increased levels of atmospheric carbon dioxide (CO2) may actually help temper the negative impacts of climate change. Indeed, plants require CO2 for photosynthesis. The gas also tends to enhance plant drought tolerance and contributes to the accumulation of soil organic matter. What remained unclear until recently was whether the benefits of higher CO2 levels would be maintained during extreme climatic events. However, an answer has just been found by INRA and CNRS researchers, who carried out a large-scale experiment at the CNRS Ecotron facility in Montpellier. Forty-eight large samples of upland grassland—blocks with a surface area of 1 m2 and a depth of 60 cm—were excavated in the Auvergne region of France. They were then subjected to different experimental treatments to test the effects of temperature, rainfall, atmospheric CO2, and the presence or absence of severe drought and heat. Present conditions were compared to the hotter and drier conditions predicted to occur as of 2050.

The study revealed that, during simulated droughts and heatwaves, elevated levels of atmospheric CO2 helped buffer the effects of thermal and water stress experienced by grassland plant species, allowing them to maintain their physiological functions. Root growth was stimulated, allowing plants to capture more water and nutrients from the soil, promoting regrowth once conditions returned to normal.

When it came to net carbon assimilation, the researchers discovered that the benefits associated with increased CO2 levels completely canceled out the negative effects associated with extreme climatic events. The results demonstrate that it is crucial to fully examine ecosystem interactions when studying the potential impacts of climate change. They also indicate that increased levels of atmospheric CO2 can enhance the resilience of soil organic matter and grassland ecosystems, thus limiting the effects of droughts and heat waves on livestock systems. However, these findings do not speak to the cumulative impacts that may result from repeated extreme events, an issue that will need to be examined using modeling approaches.

View of the inside of an Ecotron macrocosm containing 4 blocks of grassland.. © INRA, C. Picon-Cochard
View of the inside of an Ecotron macrocosm containing 4 blocks of grassland. © INRA, C. Picon-Cochard

Contact(s)
Scientific contact(s):

Press Relations:
INRA News Office (33 (0)1 42 75 91 86)
Associated Division(s):
Forest, Grassland and Freshwater Ecology
Associated Centre(s):
Auvergne-Rhône-Alpes

Reference

Roy J, Picon-Cochard C, Augusti A, Benot ML, Thiery L, Darsonville O, Landais D, Piel C, Defossez M, Devidal S, Escape C, Ravel O, Fromin N, Volaire F, Milcu A, Bahn M, Soussana J-F. 2016. Elevated CO2 maintains grassland net carbon uptake under a future heat and drought extreme. PNAS, 16 May 2016. DOI: 10.1073/pnas.1524527113