Understanding how species shifts affect ecosystem functioning is a fundamental goal of ecosystem ecology. Tree species effects on carbon (C) and nitrogen (N) cycling are largely driven by the dominant species’ functional traits, reflecting both the plant’s evolutionary history and its plastic responses to the environment. Yet, most research to date has focused on aboveground plant traits and far less is known about the importance of root interspecific variation in driving soil C and N cycling. We examined patterns in fine root production (FRP) under ectomycorrhizal-(ECM) and arbsucular mycorrhizal-(AM) tree species in multiple eastern U.S. forests. We quantified FRP with two types of root-ingrowth cores: cores filled with native soil (quantifying growing-season root production) and cores filled with C4 corn-field soil carrying an enriched δ13C signature compared to C3plant-derived material (quantifying total rhizodeposition). We predicted FRP under ECM compared to AM species, both due to plant trait and soil property differences associated with these distinct mycorrhizal groups. Further, we hypothesized there would be greater rhizodeposition per unit root mass under ECM compared to AM trees due to greater reliance on mycorrhizal hyphae and root exudates for nutrient uptake.
Results/Conclusions
Overall, we found significant differences in both root production and rhizodeposition among our focal tree species and across sites. While root production alone did not vary between mycorrhizal groups, we did find evidence for greater rhizodeposition under ECM compared to AM tree species. Our results emphasize how different tree species can employ distinct C allocation strategies belowground, and how such species patterns may differentially influence soil C inputs across a landscape. Additionally, tree species appear to both respond to and reflect their soil environment. As global change induces broad-scale species shifts, incorporating such species variation in ecosystem models will be important to accurately predict terrestrial carbon-climate feedbacks.