Plant legacies and soil microbial community dynamics control soil respiration

Through litter and root inputs, plants modulate soil properties and the soil microbial communities around them. In turn, these changes in soil properties and microbial community composition can impact plant performance (i.e., plant-soil feedbacks). Many studies have focused on how plant-soil feedbacks affect plant performance and successional patterns, but studies on the impact of plant-soil feedbacks on ecosystem processes are rare. Our research focused on the potential of species-specific plant-soil feedbacks to affect rates of soil organic matter (SOM) decomposition. We conducted a “home vs. away” plant-soil feedback greenhouse experiment using two C₃ grass species (Bromus inermis and Pascopyrum smithii) grown in C₄ tallgrass prairie soil. We used a closed-circuit CO₂ trapping method and isotopic analysis to differentiate between root-derived and SOM-derived CO₂ production. Contrary to our predictions, plant-soil feedbacks on plant biomass were independent of the effects of plant-soil interactions on SOM-derived CO₂ production, but we did detect a significant legacy of conditioning by B. inermis on subsequent total belowground respiration (i.e., total belowground respiration was higher in soils originally conditioned by B. inermis regardless of which plant species was currently growing in those soils). We attribute these results to the differential effects of these plant species on soil chemistry and soil microbes during the original conditioning phase. This is supported by the observation that differences in soil chemistry and bacterial community composition persisted in soils conditioned by different plant species throughout the entire experiment. Together these results suggest that plant-soil history is important for soil respiration and that differences in soil microbial communities induced by conditioning with different plant species may have lasting effects on ecosystem processes.