Individual versus combined effects of elevated CO2, warming and drought on grassland functioning – synthesis from a multiyear experiment

In a rapidly changing world, ecosystems are increasingly affected by a simultaneous rise in atmospheric CO₂ concentrations, temperature and drought events. While the individual effects of these global change factors on ecosystems are comparatively well understood, there is a major lack of experimental studies examining their interactive effects. In a multifactor experiment (ClimGrass) established in 2013 on a managed montane grassland in Central Austria we tested how elevated CO₂, warming and drought individually and interactively affect ecosystem processes underlying carbon, nutrient and water cycling.

This talk will present an overview of key findings from the ClimGrass experiment. Future climate conditions (3 °C warming and + 300 ppm atmospheric CO₂) synergistically amplified drought effects on ecosystem CO₂ and water fluxes, on plant growth and phenology as well as belowground carbon allocation. Non-additive effects of interacting global change factors were also observed for microbial communities and processes related to soil carbon and nitrogen cycling. Furthermore, future conditions altered the recovery of ecosystem fluxes from drought, and changed the dynamics of soil water retention and grassland water use. Overall, the findings from ClimGrass suggest that multiple interacting global change factors lead to complex non-additive effects with major consequences for ecosystem functioning in a future world.