DOI: 10.5061/dryad.14328
title: Data from: When mutualisms matter: Rhizobia effects on plant communities depend on host plant population and soil nitrogen availability

description: 1.Mutualistic interactions, such as the relationship between legumes and
 rhizobia, can affect community properties, yet there needs to be greater
 understanding of when these interactions may be most important to
 communities. Resource mutualism theory provides predictions based on
 variation in abiotic and biotic factors. First, 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. Rhizobia likely have
 greater community impacts when associating with hosts that benefit greatly
 from rhizobia, produce many nodules, and fix a lot of nitrogen. Second,
 increased soil nutrient availability typically reduces the partner
 benefits of legume-rhizobium interactions. As a result, the
 legume-rhizobium resource mutualism may have greater effects on
 communities in low nitrogen environments. 2.We first conducted a common
 garden study of the annual legume Chamaecrista fasciculata to explore
 intraspecific variation in focal traits related to competition and
 mutualistic interactions with rhizobia. Then, we manipulated the presence
 of rhizobia, nitrogen fertilization, and population identity of C.
 fasciculata in mesocosms simulating native plant communities. We measured
 plant diversity, assessed changes in community composition, and measured
 soil nutrient availability. 3.We detected significant genetically-based
 intraspecific variation in growth and mutualism related traits across C.
 fasciculata populations. From the experimental mesocosms, we found that
 although rhizobia consistently reduced diversity, rhizobia most strongly
 reduced diversity when associating with C. fasciculata populations that
 were highly dependent on rhizobia and when nitrogen was most limiting. We
 also detected greater variation among populations in their effects on
 communities in the absence of rhizobia; the presence of rhizobia
 dramatically minimized effects of population identity on the surrounding
 community. 4.Synthesis. These findings show that abiotic environmental
 factors and intraspecific variation in a dominant host plant can influence
 the magnitude of mutualism effects on communities and, reciprocally, how
 the presence of key mutualists can influence the importance of
 genetically-based variation among populations to community outcomes. While
 prior studies have detected both strong and weak effects of mutualism on
 plant communities, our study illustrates that mutualism theory may predict
 when strong mutualism effects are most likely to occur and also shows how
 theories developed for particular species interactions may make studies
 investigating the ecological impacts of genetic variation a more
 predictive science.
description: When mutualisms matter:
 DataData from the
 experimental greenhouse mesocosms described in the manuscript: When
 mutualisms matter: rhizobia effects on plant communities depend on host
 plant population and soil nitrogen availability.JEcol Dryad
 Data.xlsx