While research on plant species' influence on ecosystem properties and processes has focused on exotic species introductions, little is known about how reintroductions of extirpated species may impact degraded systems. This study examines how the reintroduction of C4 grasses into former prairie-savanna systems influences soil carbon (C) and nitrogen (N) cycling relative to unmanaged successional communities dominated by exotic C3 grasses at two sites in southwestern Michigan, USA. The C4 and C3 species examined in this study differ significantly in many traits that are expected to influence soil C and N cycling. C4 species had significantly greater root and shoot biomass, and more recalcitrant tissue compared to the dominant C3 species. Soils under C4 species had significantly lower inorganic N levels, and lower in situ net N mineralization rates than soils under C3 species. Plant shoot decomposition rates were significantly slower for C4 species compared to C3 species. We also found limited evidence for increasing soil C pools under C4 species after 12 years. Overall, our results show that species that possess different plant traits relevant to soil C and N cycling can indeed alter soil processes on a decadal timescale. Given the increasing extent of human impacts on plant communities, expanding our understanding of how plant species changes are likely to impact ecosystem properties is imperative to evaluating which species shifts have the most potential to alter ecosystem function.