Abstract
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.
Highlights
Ecologists are increasingly using plant traits for explaining and predicting ecosystem functioning
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
These four species represented two grasses and two herbs of differing growth strategies, with, of the grasses, A. odoratum being slower growing than D. glomerata, and, of the herbs, L. hispidus being slower growing than R. acetosa
Summary
Ecologists are increasingly using plant traits for explaining and predicting ecosystem functioning. These approaches generally use the leaf economics spectrum (Wright et al 2004), where exploitative leaf traits that maximise photosynthesis, such as high specific leaf area and leaf nitrogen content, maximize plant growth and nutrient uptake, and accelerate rates of soil nutrient and carbon cycling Ecologists have shifted their focus from aboveground plant functional traits to belowground traits for explaining soil and ecosystem processes (Bardgett et al 2014). Root traits are increasingly used to predict how plants modify soil processes. 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
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