Combined elevated CO2 and climate warming induces lagged effects of drought in Lolium perenne and Plantago lanceolata

Future climate scenarios predict increases in elevated atmospheric CO2, air temperature and drought, but the impacts of multiple climate change factors on ecosystem functioning remain unclear. In this study, we compared drought responses of plants under future versus current climate conditions. In addition to focusing on stress during the drought itself, we also examined post-drought lagged effects, and whether warming and elevated CO2 alter these. We grew monocultures and mixtures of two grassland species (Lolium perenne L. and Plantago lanceolata L.) in four simulated climate scenarios: (1) current climate, (2) current climate with drought, (3) warmer temperature with drought and (4) combined warming, elevated CO2 and drought. L. perenne and P. lanceolata were influenced by the climate scenario but not differently enough to modify the competitive balance. Warming aggravated drought impacts on L. perenne and elevated CO2 only partly compensated for these effects. In a warmer climate, with or without elevated CO2, drought continued to enhance senescence and mortality in L. perenne long after the water shortage, while such lag effects were not observed in current climate. In P. lanceolata, a similar stimulation of senescence and mortality was induced, but only under combined warming and elevated CO2. These lag effects induced by the future climate may reduce resilience.