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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While the spread of the exotic Lythrum salicaria L. across wetlands in North America is thought to negatively affect the performance and diversity of native species, the actual impacts of L. salicaria invasion on community dynamics and ecosystem properties are not well understood. To determine whether L. salicaria affects community aboveground biomass, native species biomass, or soil properties, we studied two common situations in central New York State where L. salicaria invaded (i) an abandoned agricultural field and (ii) a relatively pristine wetland with low species diversity. In the agricultural site, nearly monospecific stands of L. salicaria and Phalaris arundinacea L. had nearly identical shoot mass (approx. 850 g·m–2) but divergent soil characteristics. Inorganic nitrogen was significantly higher under L. salicaria than under P. arundinacea. The low-diversity site is dominated by Carex lacustris Willd., with distinct areas codominated by either L. salicaria or Typha latifolia L. In this site, we found that areas with a codominant species had significantly more total aboveground biomass than those dominated by C. lacustris, suggesting that L. salicaria invasion does not significantly lower native species biomass. However, most soil nutrient levels did not differ among vegetation zones, indicating that species composition changes did not alter soil properties in the short term. This study supports a growing literature suggesting that L. salicaria invasion may not negatively impact relatively pristine wetlands as previously believed.

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Plant species can both directly and indirectly affect soil processes in various ways, including through functional traits related to the quantity and chemistry of biomass produced. Understanding how functional traits affect soil processes may be particularly important in restorations that specifically select a target plant community. In this study, I examined how species differing in litter traits alter decomposition, both directly via chemistry and indirectly via influences on soil microclimate. Decomposition dynamics of two old-field grasses were compared with the native prairie grass, Andropogon gerardii, in two Michigan old-fields. Decomposition rates were strongly, negatively related to tissue chemistry, but showed little effect of microclimate differences. Soil bacterial community composition differed between species at one site, while extracellular enzyme activities differed between species at the other site. These findings suggest plant species may be altering microbial community function. Overall, litter chemistry was the dominant factor determining decomposition rates, suggesting that restoring native prairie grasses with recalcitrant litter into grass-dominated old-fields could slow litter decomposition and ultimately lead to changes in soil carbon and nitrogen cycling. Eventually, this could lead to soils that more closely resemble the more organic-rich soils of native prairies and ultimately increase prairie plant community restoration success.