Plant communities drive belowground responses to drought
Recent evidence suggests that plants modify belowground communities through their functional traits, and that root traits in particular play an important role through the supply of carbon (C) to soil organisms via their exudates. Moreover, evidence suggests that by modifying soil C supply, different plant species have the potential to affect the response of belowground communities to disturbances such as extreme drought.
We hypothesised that greater root biomass and dominance of root traits associated with increased soil C supply leads to greater stability of belowground communities and processes under drought. To test this hypothesis we set up a field-based mesocosm experiment, in which we varied the evenness and identity of dominant species of plant communities consisting of four grassland species that strongly differ in their ecological strategies and root traits (Anthoxanthum odoratum, Dactylis glomerata, Leontodon hispidus, and Rumex acetosa). We imposed an experimental drought, and measured the response of plant and soil communities, and processes of C and nitrogen (N) cycling, before, at the end, and two and eight weeks after ending the drought.
Drought had long-lasting effects on both plant and soil communities, and these effects were modified by the identity of dominant plant species in model communities. While both plant communities and soil microbial communities had not recovered completely two months after ending the drought, most ecosystem processes (respiration, net ecosystem exchange, CH4 and N2O emissions) returned to control levels. However, using structural equation modelling, we found that plant communities strongly modified soil microbial communities and their response to drought, and that in turn, these changes had cascading effects on ecosystem processes. We conclude that plants, through their root traits and belowground C inputs, drive ecosystem response to drought.