Plant-soil feedback and species coexistence: interactions among soil pathogens, irradiance, and species life histories

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Ecologists have long been puzzled about how so many tree species can coexist within a given forest. The main goal of the project is to link two seemingly unrelated and competing mechanisms that have been proposed for tree species coexistence. These are how tree species respond to light availability and to increasing density or proximity of other individuals of the same species. Tree seedling response to soil fungi may hold the key to tree seedling response to light availability and densities of other individuals of the same species. Seedling mortality to soil pathogens associated with their own species is likely enhanced in low light environments for many species, and much more prevalent in species considered 'shade intolerant'. In addition, these biotic plant-soil feedbacks may play a large role in heightening differences among species in their responses to light. This research may help to better define shade tolerance and explain tree species coexistence; both results are vital for effective conservation and management of temperate forests. For instance, results may have implications for forest restoration or the timber industry with regards to tree species with specific light requirements or regeneration difficulties. Additionally, this project will educate, train and mentor undergraduate students in plant and soil microbial ecology as well as provide public outreach to local K-12 teachers and students. The primary goal of the project is to investigate biotic plant-soil feedbacks that can affect distance- and density-dependent seedling survival and growth across light gradients and among tree species with varying life-history traits. The researchers will employ a novel field-based transplant experiment using fungal exclusion pots, which will investigate the mechanisms of tree seedling response to: 1) feedbacks between plants and the soil microbial community as a function of light availability, and 2) response to low light as a function of these feedbacks for eight temperate tree species that vary in seedling shade tolerance, local adult abundance and association with arbuscular and ectomycorrhizal fungi. Thus, this research will investigate the degree to which plant-soil feedbacks contribute to species coexistence through not only negative-density dependent processes, but also as a driver of species light gradient partitioning. The project will also investigate which factors (e.g., soil pathogen density and composition, and/or seedling traits) contribute to greater negative effects from disease and plant-soil feedback in low light.