The factors structuring terrestrial plant communities remain an essential problem within ecology. A growing body of work has identified important roles of soil organisms in plant species coexistence and turnover during succession. Arbuscular mycorrhizal (AM) fungi, symbionts associating with most plant species and facilitate resource uptake, may be particularly important as previous work has shown strong effects of manipulation of the presence, composition and diversity of AM fungi on plant communities. Previous theory identifies that AM fungal dynamics could drive positive or negative feedbacks between plant species, with very different implications for the influence of AM fungi on species turnover during succession. In the case of positive feedback, AM fungal dynamics could alternatively inhibit or reinforce species turnover during succession, depending on starting conditions. In the case of negative feedback, AM fungal dynamics would move the plant community toward an equilibrium composition, regardless of initial conditions. We investigate the dynamics of AM fungi within the context of plant species turnover and coexistence during succession within tallgrass prairie by integrating results from experiments, field trials and theory.
Greenhouse inoculation studies demonstrate that late successional prairie plant species are more responsive to AM fungi than early successional species. Late successional prairie plant species are also significantly more sensitive to the species identity of AM fungi. These results are consistent with the success of late successional plants depending upon mycorrhizal fungal dynamics. In support of this possibility, we find that reintroduction of AM fungi derived from late successional prairies improves establishment and growth of late successional prairie plant species in field trials. We also find that late successional prairie plant species preferentially allocate carbohydrates to the most effective AM fungal species. Together, these results suggest that AM fungal dynamics are likely to generate positive feedback between early and late successional plant species. We explore these potential dynamics with analytical theory and simulations, and characterize conditions in which AM fungal community dynamics inhibit succession or facilitate species turnover.