Previous research has shown that interactions between plants and soil microbes can provide a mechanism that could be driving patterns of plant biodiversity both though positive and negative feedbacks. Positive feedback is expected to lead to a loss of species diversity, while negative feedback leading to coexistence. Interactions with mutualists, such as arbuscular mycorrhizal (AM) fungi, are generally thought to generate positive feedbacks, however asymmetric fitness relationships between hosts and their mutualists can create scenarios where mutualisms generate negative feedback. We conducted a series of 2 phase growth assays to measure the fitness impacts between 38 plant species and 7 species of AM fungal species. In Phase 1 training plants were inoculated with a homogeneous AM fungal community that was then allowed to differentiate. These differentiated communities were then used as inocula in a growth assay (Phase 2). These crosses allowed us to measure the intensity of the mycorrhizal feedbacks on the plants. We tested the dependence of these feedbacks on plant phylogenetic relationships and life history characteristics. The objective of this study is to build a predictive framework for understanding the impacts of AM fungi on plant diversity and coexistence, using the tallgrass prairie system as a model.
Results/Conclusions
Amplicon sequencing of the large ribosomal sub-unit (LSU) has been completed for the first and second year’s soil samples (Phase 1). Analysis shows that AM fungal communities are different across host plant species (P<0.001) and family (P<0.001). We analyzed the mycorrhizal responsiveness, the ratio of biomass between plants in live and sterile soil, of each host plant to the differentiated AM fungal communities (Phase 2). We tested whether species experienced greater fitness benefits when grown in home soil trained on the same plant family, (positive feedback) or in away soil trained on a different plant family (negative feedback). Host plant family was an important factor in the analysis, with host plant families differing in both the strength and direction of the feedback effects (P=.006). We also found the strength and direction of the feedback affects between early and late successional plants varied across current host plant family (P=0.021). The analysis shows that fitness relationships are not symmetric between all plants and their associated soil communities. The importance of plant family as an interacting factor leads us to the conclude that whether plant species are predicted to coexist will be highly dependent on phylogenetic relationships.