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 C(4) prairie grasses affected soil C and N cycling 11 years after reintroduction into successional old-field communities dominated by non-native C(3) 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 C(4) species compared under C(3) species. As predicted, the C(4) species had greater biomass and more recalcitrant tissue [higher C:N, acid detergent fiber (ADF):N] compared to the dominant C(3) species. The three C(4) 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 C(4) species did not differ in inorganic N levels, but levels were lower than in soils under the C(3) species, and soils under Andropogon had slightly lower in situ net N mineralization rates compared to those under C(3) species. We found little evidence of larger surface soil C pools under C(4) species versus C(3) species after 11 years and no differences in subsurface soil C or N among species. The C(4) species contributed a significant amount of C to both soil depths after 11 years. Our results demonstrate that C(4) species reintroduction into old-fields can alter C and N cycling on relatively short timescales, and that individual C(4) 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.

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Many factors influence which plant species are found in a particular wetland. The species pool is composed of the species present in the seed bank and species able to disperse into the wetland, and many abiotic and biotic factors interact to influence a species performance and abundance in the plant community. Anthropogenic activities produce specific stressors on wetland systems that alter these abiotic and biotic interactions, potentially altering species composition. We simulated three common wetland hydrogeomorphic ͑HGM͒ subclasses in a greenhouse to examine the effects of two stressors-sedimentation and nitrogen ͑N͒ enrichment-on the performance of 8 species grown in artificial communities. Species establishment, height, biomass, and foliar N and P concentrations were measured to explore species responses to stressors and competition, as well as the potential impacts of changes in species composition on ecosystem processes. Species were affected differently by sedimentation and N enrichment, and there were differences in overall community sensitivity to stressors between wetland subclasses. Sedimentation generally reduced seedling establishment, while N enrichment produced variable effects on height and biomass. Interspecific competition had little effect on establishment but significantly reduced most species biomass. Sedimentation generally lowered community biomass, diversity, and richness, while enrichment increased community biomass. Establishment, biomass, and foliar nutrient concentrations significantly differed between many species, suggesting that shifts in species composition may impact ecosystem processes such as nutrient cycling and carbon storage. Phalaris arundinacea, an aggressive clonal graminoid, universally dominated all wetland subclasses. This dominance across a range of environmental conditions ͑sedi-mentation, fertility, and hydrology͒ has important implications for both restoration and predicting the impacts of human activities on species composition. Our results suggest that, in regions where P. arundinacea is common, restoration projects that establish communities from seeds and human activities that cause vegetation removal are likely to become dominated by P. arundinacea.

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