Diez, JeffPatel, Macy2024-09-202024-09-202023-06https://hdl.handle.net/1794/3008322 pagesThe mutualism between legume species and rhizobia has long been acknowledged as a vital part of plant community dynamics in both natural and agricultural systems. Increasing anthropogenic nitrogen inputs can alter this mutualism and in tum plant commm1ity dynamics. Still, few studies have explored the dependencies of these resource-based mutualistic microbes, rhizobia, on ambient nitrogen levels, and how this may affect competition between hosts and neighboring plants. To test the potential nitrogen-dependent role of rhizobia in mediating coexistence between legumes and non-legumes, we conducted a competition experiment in the greenhouse replicated across rhizobial inoculation and nitrogen fe1tilization treatments. Here, we employ contempora1y ecological theo1y to assess how rhizobia and nitrogen fertilization influence niche differences and fitness inequalities determining competitive outcomes. We measured the fecundity of plants across a competition gradient to parameterize annual plant population models and to use these parameter estimates to predict the outcomes of competition between our plant species. We found that both nitrogen and rhizobia shift the probability of coexistence, and further that the effect of rhizobia was dependent on nitrogen concentration. We also found that these results differed when legumes were competing with either other legumes or non-legumes. These results suggest that these context-dependent mutualisms are impo1tant in dete1mining competitive outcomes. Further, this study sheds light on the ways anthropogenic nitrogen inputs are likely to shift community composition and diversity of native plants and microbial communities alike.en-USUO theses and dissertations are provided for research and educational purposes and may be under copyright by the author or the author’s heirs. Please contact us <mailto:scholars@uoregon.edu> with any questions or comments. In your email, please be sure to include the URL and title of the specific items of your inquiry.Rhizobiacoexistence outcomeslegumesThesis