Janzen and Connell described ecological mechanisms by which host-specific natural enemies promote community diversity by facilitating the proliferation of heterospecifics in the vicinity of the focal host species. This "negative feedback" theory forms the conceptual framework of this investigation testing plant and soil-microbe interactions, which have been overlooked for years by ecologists. Soil microbes have numerous negative and positive effects on plant fitness, and their fundamental importance to plant populations and community structure is now widely accepted but poorly understood. This project is a continuation of research into the negative feedbacks of soil-borne fungal pathogens on black cherry recruitment and population dynamics. Field surveys will be conducted to determine the survival of black cherry seedlings in early, mid, and late successional sites. To assess the degree of host-specificity of the fungal pathogen (Pythium), seeds from black cherry and other plant species will be germinated in the laboratory in sterile and Pythium-inoculated agar. Similarly, seeds from ten plant species will be germinated in sterile and inoculated soils under greenhouse conditions. Results from the field, laboratory and greenhouse studies will be compared with data collected on natural plant distributions in the field. The ultimate objective is to determine the role played by soil-borne pathogens in seedling establishment, spatial distributions, and successional change. This research can substantially advance our limited knowledge about how these complex and long-overlooked interactions influence community diversity and succession.
