Background/Question/Methods Host specific divergence in mycorrhizal communities can feed back on plant fitness and affect plant community structure. Symmetric fitness relationships between plants and mycorrhizal fungi can generate positive plant-soil feedbacks, leading to a loss of species diversity over time. Alternatively asymmetry in fitness relationships between plants and mycorrhizal fungi can generate negative feedbacks, resulting in a more diverse community. We tested the divergence of arbuscular mycorrhizal (AM) fungal communities and the resulting feedbacks on plant fitness in among 38 prairie plant species. Replicate pots of each of the 38 plant species were inoculated with a common mixture of seven AM fungal species and grown over two growing seasons. AM fungal composition was monitored using amplicons sequencing targeting the LSU. Feedback test experiments were conducted after the second growing season that tested the relative performance in their own and other trained AM fungal communities. We tested the importance of plant phylogeny and life history on patterns of AM fungal divergence and on strength and direction of plant soil feedback. Results/Conclusions AM fungal communities differed significantly across host plant species, with plant phylogenetic distance and the interaction of plant phylogeny and plant life history being important predictors. The strength of feedback on plant fitness depended on plant family and plant life history. Fabaceae hosts had the greatest mean responsiveness when grown in soil trained with the same species, showing evidence of positive feedback. Poaceae hosts had the strongest feedback effects when grown in soil that was trained on plant from another family showing evidence of negative feedback. Asteraceae hosts did not show strong evidence of an interaction with previous host plant family. Host plants also showed negative feedback effects when species with high mean responsiveness were grown in soil that was trained with a highly responsive species. This effect differed between plant families with Poaceae showing the smallest negative effect and doing best when the previous host was of a different plant family. Fabaceae and Asteraceae had similar negative feedbacks from highly responsive hosts, though Asteraceae did best when the previous host was of a different family, and Fabaceae did best when the previous host was the same family. Our results show that fitness relationships between plants and mycorrhizal fungi are not symmetric and that the resulting feedback dynamics can contribute to plant species coexistence.
