COS 12-5
Intraspecific variation in legume-rhizobium mutualist partners affects species interactions
Mutualisms can drive population dynamics and evolutionary processes, but effects can also extend beyond the partners to influence communities. The legume-rhizobium mutualism can directly and indirectly affect species interactions through changes in competition and nutrient dynamics. My previous work shows that rhizobia act as a keystone mutualist in this system, facilitating the establishment of Chamaecrista fasciculata and as a result, reducing diversity, altering community composition, and driving convergence in community assembly. However, there is substantial intraspecific genetic variation in how legumes interact with rhizobia, including variation in legume growth response to rhizobia, number of rhizobia-housing nodules, and nitrogen fixation. Therefore, not only can the presence of a particular legume species and its associated rhizobia influence the surrounding community, but the genetic identity of the colonizing legume or rhizobia, and potentially even coevolutionary interactions between partners could also alter community processes. Through a series of experiments manipulating the genetic identity of the legume and the rhizobia, I explore: 1) How legume and rhizobium populations may be locally co-adapted to each other; 2) How intraspecific variation associated with the legume-rhizobium mutualism and coadaptation can affect species interactions and community dynamics.
Results/Conclusions
C. fasciculata populations differed in their effects on communities with some populations becoming more dominant than others. The magnitude of these effects depended on the presence of rhizobia. Rhizobia typically reduced diversity and increased community convergence, and the reduction in diversity and change in community structure appears to be largely driven by C. fasciculata dominance, with populations that benefit more from rhizobia reducing diversity more in the presence of their mutualist. In the absence of rhizobia, there was greater dissimilarity in beta diversity among populations. Moreover, soil source location also drove differences in C. fasciculata growth and nodule production, indicating variation in soil communities across sites that may affect plant responses to the environment. These findings expand our understanding of plant community dynamics by incorporating the effects of positive symbiotic interactions on plant communities and how communities are influenced by intraspecific variation in traits related to species interactions. They also further expand the linkages between ecology and evolution in communities by testing for coadaptation between mutualists across a broad geographic scale.