Nitrogen (N) addition is predicted to destabilize the legume-rhizobium mutualism. Lau and Heath have previously found data to support this theoretical prediction for the rhizobium partner. The potential role of evolution in the legume host in response to N-addition, or how N-addition will alter the coevolutionary feedbacks between leguminous hosts and their rhizobium symbionts, remain unaddressed. Jen Lau, Katy Heath, and Mia Howard will use approaches from quantitative genetics to investigate the potential for host evolutionary responses to N and to evolutionary changes in their rhizobium partners. Their initial project will identify the extent of plant genetic variation in traits underlying symbiotic interactions with rhizobia and predict evolutionary responses of plants to both N and rhizobium genetic variation. The goal is to begin to better understand the responses of the plant component of this series of nested mutualisms and the potential for coevolution between the plant and rhizobium partners. These results and generated plant lineages will lead to further experiments assessing how plant evolution feeds back to influence interactions with other community members and rhizobium evolution.