Plants are the critical link between aboveground and belowground processes. Through their litter and root inputs, plants modulate soil properties and soil microbial communities around them. In turn, these changes in soil properties and microbial community structure 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. In forested systems, leaf litter decomposes most quickly under the plant species from which it was derived suggesting that soil biota become conditioned to the aboveground inputs of trees (i.e., home-field advantage). However, few studies have investigated how feedbacks between the plant roots and soil biota can affect ecosystem processes, such as decomposition of stored soil organic matter (SOM). The overall objective of our research was to investigate how species-specific plant-soil feedbacks affect rates of SOM decomposition. We addressed this by conducting 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 mineralization.
Results/Conclusions
There was a significant positive plant-soil feedback on total plant biomass for B. inermis at the end of the first round of the greenhouse experiment while there was a significant negative plant-soil feedback for P. smithii. Feedback effects were not significant during the second round. Total belowground respiration rates only differed significantly in the second round. For B. inermis, total belowground respiration was marginally higher when it was grown in its home soils. However, the opposite pattern was true for P. smithii. During the second round, SOM-derived CO2 production was always significantly higher in soils that were originally conditioned by B. inermis regardless of which plant species was being grown in those soils. Unplanted soils that were originally conditioned by B. inermis also had significantly higher mineralization rates. Our results are likely due to the differential effects of plant species on soil microbes during the original conditioning phase. This hypothesis is supported by the observation that microbial biomass was significantly higher in soils conditioned by B. inermis. Together these results suggest that plant-soil history is important for SOM mineralization and that changes in soil microbial community caused by shifts in plant species composition can have lasting effects on ecosystem processes.