Elevated CO2 and warming effects on grassland plant mortality are determined by the timing of rainfall

Global warming is expected to increase the mortality rate of established plants in waterlimited systems because of its effect on evapotranspiration. The rising CO2 concentration ([CO2]), however, should have the opposite effect because it reduces plant transpiration, delaying the onset of drought. This potential for elevated [CO2] (eCO2) to modify the warming effect on mortality should be related to prevailing moisture conditions. This study aimed to determine the impacts of warming by 2 C and eCO2 (550 µmol mol ¹) on plant mortality in an Australian temperate grassland over a 6-year period and to test how interannual variation in rainfall influenced treatment effects.