Impacts of C₄ grass introductions on soil carbon and nitrogen cycling in C₃-dominated successional systems

While recent research has focused on the effects of exotic plant species on ecosystem properties, less is known about how restoring individual native plant species, differing in biomass and tissue chemistry, may impact ecosystems. We examined how three native C₄ prairie grasses affected soil C and N cycling 11 years after reintroduction into successional old-field communities dominated by non-native C₃ grasses. The species examined in this study differ in traits that are expected to influence soil C and N cycling (biomass and tissue chemistry). Thus, we hypothesized that cycling rates would decrease, thereby increasing pool sizes in soils under C₄ species compared under C₃ species. As predicted, the C₄ species had greater biomass and more recalcitrant tissue [higher C:N, acid detergent fiber (ADF):N] compared to the dominant C₃ species. The three C₄ species did not differ in tissue C:N, ADF:N, or root biomass, but Andropogon had more than twice the shoot biomass of Schizachyrium and Sorghastrum. Soils under the C₄ species did not differ in inorganic N levels, but levels were lower than in soils under the C₃ species, and soils under Andropogon had slightly lower in situ net N mineralization rates compared to those under C₃ species. We found little evidence of larger surface soil C pools under C₄ species versus C₃ species after 11 years and no differences in subsurface soil C or N among species. The C₄ species contributed a significant amount of C to both soil depths after 11 years. Our results demonstrate that C₄ species reintroduction into old-fields can alter C and N cycling on relatively short timescales, and that individual C₄ species differ in the magnitude of these effects. Improving our understanding of how species influence ecosystem properties is essential to predicting the ecosystem-level consequences of plant community alterations due to land use changes, global change, and species introductions.