Root-derived soil carbon (C) influx is a critical process that connects two major pools of C in the planet—atmospheric CO2 and soil C. A fundamental paradox in terrestrial biogeochemistry is that root C influx to soil can either provide a net C sink by promoting soil C stabilization, or it can stimulate the loss of existing soil C through enhanced microbial degradation of soil organic C. It is uncertain which direction will dominate in the future, because we do not understand which root traits control root-C influx, and how changes in root-C influx in-turn affect decomposition processes and ultimately soil C stabilization. Using Panicum virgatum(switchgrass) as a model plant in field studies and controlled laboratory incubations, we explored how intraspecific differences in root traits affect root-derived C influx, microbial community composition, and soil organic C dynamics.
Results/Conclusions
We found that subtle differences in specific root length (SRL) among cultivars of Panicum virgatum (switchgrass) influenced the rate of soil C input through exudation, with a positive correlation between SRL and plant-derived C recovered in soil four years following establishment. In addition, the active microbial community composition and rhizodeposit C uptake varied among cultivars, and reflected differences in root structure. Finally, root structure impacted root turnover and decomposition, where a relative increase in the abundance of roots in the smallest diameter size class enhanced root decomposition rates, but reduced SOC decomposition rates. These data suggest that root traits importantly affect root C influx, microbial activity, and soil C stabilization and destabilization processes.