This thesis is comprised of three studies evaluating whether shifts in soil or plant communities affect each other as well as ecosystem processes. I used contrasting fire regimes and a plant species invasion to test hypotheses regarding the biological effects of composition on decomposition, plant species effects on ecosystem functioning, and root-associated bacterial relationships with plant species. All studies were conducted at the Konza Prairie Biological Station (KPBS), a representative tallgrass prairie ecosystem of the United States. I compared soil biota effects on decomposition and decomposition stability in burned and unburned prairie. Upon assessing effects of soil biota composition on decomposition rates and decomposition stability of various surface and buried substrates, I found no consistent effect of community composition on decomposition or decomposition stability. Rather, a complex interaction between community composition and substrate type mediated responses. Burn regimes influenced the effects of soil communities on decomposition stability and suggested effects on functional stability should be considered when managing ecosystems. The second and third studies used the invasion of Andropogon bladhii, a C4 grass species, onto KPBS to examine whether displacement of a native C4 dominant (Andropogon gerardii ) by the non-native C4 species affects ecosystem properties and community structure. I measured plant species diversity, pools and cycling rates of C and N in native and invasive dominated sites. The invasive species imposes spatial heterogeneity in soil properties, creates a potential to decrease ecosystem N availability, and reduces plant species diversity. A positive response to burning exacerbates this species' ecosystem effects and thwarts management practices to exclude invasive species. Finally, I compared root-associated bacterial communities of each plant species in the first known study to use a molecular phylogenetic approach to examine root-bacteria in a non-agriculture system. The two plant species harbor similar bacteria groups when examined at a broad taxonomic scale; but distinct communities are evident when compared at finer taxonomic resolutions. A large effect on root bacteria as a possible invasion mechanism was not evident, however, the role of these bacteria in assisting the invasive plant in altering biogeochemical properties of the prairie cannot be ruled out.