Soil Pathogen-Mediated Coexistence of Tree Species

Michigan State University, East Lansing MI

Investigators

Abstract

Intellectual merit: As an explanation for the maintenance of tropical tree diversity, Janzen (1970) and Connell (1971) proposed that natural enemies reduce seedling recruitment in the vicinity of conspecific adults and/or at high conspecific seedling density while allowing for heterospecific recruitment to occur. Numerous studies have documented mortality patterns consistent with the Janzen-Connell (J-C) hypothesis, without identifying particular causes. Soil fungal pathogens are likely causal factors of density- and distance-dependent mortality because of strong host specialization, short generation times, long persistence in soil as spores, and high fecundity. Furthermore, the potential importance of disease in structuring plant communities is only now becoming more widely appreciated. The proposed experiments, with a focus on soil fungal pathogens as the mortality agent, will test fundamental assumptions of J-C, including: 1) if host-specific soil-borne fungal pathogens cause distance and density-dependent mortality in seedlings in both temperate and tropical systems; 2) the effects of light availability in mediating pathogen effects through compensation in growth and/or more rapid lignification; 3) differential pathogen sensitivity among species varying in shade tolerance; 4) differential pathogen sensitivity among species varying in local abundance, with the possibility that pathogens keep common species in check and promote diversity or alternatively that rare species are kept rare because they are more susceptible to pathogens; 5) differential pathogen sensitivity between tropical and temperate species. Broader impacts: The proposed research is highly relevant to managing conservation reserves if diseases play a role in the population dynamics of their hosts and the structure and diversity of communities that they inhabit. Also, without adequate knowledge of plant-soil pathogen interactions in 'natural' systems it is more difficult to combat the spread of exotic, invasive pathogens. The research enhances participation of underrepresented groups in science (a female doctoral candidate and a minority female student intern), provides opportunities for undergraduate internships in Costa Rica and employment in Michigan, and provides training to Costa Rican field assistants.