Grassland species root response to drought: consequences for soil carbon and nitrogen availability

Root traits are increasingly used to predict how plants modify soil processes. Here, we assessed how drought-induced changes in root systems of four common grassland species affected C and N availability in soil. We hypothesized that drought would promote resource-conservative root traits such as high root tissue density (RTD) and low specific root length (SRL), and that these changes would result in higher soil N availability through decreased root N uptake, but lower C availability through reduced root exudation. We subjected individual plants to drought under controlled conditions, and compared the response of their root biomass, root traits, and soil C and N availability, to control individuals. Drought affected most root traits through reducing root biomass. Only SRL and RTD displayed plasticity; drought reduced SRL, and increased RTD in small plants but decreased RTD in larger plants. Reduced root biomass and a shift towards more resource-conservative root traits increased soil inorganic N availability but did not directly affect soil C availability. These findings identify mechanisms through which drought-induced changes in root systems affect soil C and N availability, and contribute to our understanding of how root traits modify soil processes in a changing world.