Increasing drought recurrence and severity alter legacies on grassland carbon and water fluxes

In a future climate, drought events are expected to become more frequent and severe, with largely unknown consequences for ecosystem functioning. Based on a number of experiments in temperate mountain grasslands we show that drought recurrence, simulated for more than 16 subsequent years, altered the responses of ecosystem productivity and of carbon and water fluxes to subsequent drought. Under future conditions of recurrent drought combined with warming and elevated atmospheric CO₂ concentrations, drought severity and its impacts on grassland carbon and water fluxes were further enhanced. Moreover, under such future conditions the movement and storage of water in soil upon post-drought rewetting was substantially altered, with implications for plant water access and use. We conclude that increasing drought recurrence and severity alter their legacies on grassland carbon and water fluxes through changes in species composition as well as changes in soil structure, with cascading consequences for grassland functioning in a future world.