Nitrogen (N) enrichment causes rhizobia to evolve reduced mutualist quality, but N also decreases light availability and legume abundance. Therefore, it is unclear whether rhizobium evolution is due to the direct effects of N, indirect effects that arise over longer timescales as N-addition affects plant communities (light or legume abundance), or their interaction. GEMS graduate student Mackenzie Caple, working with Jen Lau and Katy Heath, has inoculated greenhouse mesocosms with soil from 30-year-old Kellogg Biological Station Long-Term Ecological Research (KBS LTER) N-addition or control plots and factorially manipulated light, N, and legume density to investigate the interactive roles of these factors on rhizobium evolution. They are also investigating whether rhizobium quality recovers following cessation of N enrichment. These experiments allow for the identification of selective agents responsible for observed declines in mutualism, comparison of genetic changes after selection in different environments, and investigation of the reproducibility of evolution.