Combined effects of warming and elevated CO2 on the impact of drought in grassland species

Drought is a major growth limiting factor in the majority of terrestrial ecosystems and is expected to become more frequent in the future. Therefore, resolving the drought response of plants under changing climate conditions is crucial to our understanding of future ecosystem functioning. This study responds to the need for experimental research on the combined effects of warming, elevated CO2 and drought, and aims to determine whether the response to drought is altered under future climate conditions. Two grassland species, Lolium perenne L. and Plantago lanceolata L., were grown in sunlit climate-controlled chambers. Four climates were simulated: (1) current climate, (2) current climate with drought, (3) a warmer climate with drought, and (4) a climate with combined warming, elevated CO2 and drought. Warming did not alter the drought response, neither directly through photosynthesis nor indirectly through changes in water consumption. Also for combined warming and elevated CO2 there were no effects on the plant response to drought for any of the measured parameters. However, simultaneous warming and elevated CO2 mitigated the biomass response to drought through a positive pre-drought effect on photosynthesis and biomass response. Our results indicate that a positive pre-drought effect of combined warming and elevated CO2 has the potential to compensate for drought-induced biomass losses under future climate conditions