RAPID: From microbes to new tropical forests: an experimental test of fungal specialization on host tree genotypes in the context of a reforestation experiment

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Soil fungi are thought to be one of the most important factors for establishment of tropical tree seedlings. Pathogenic soil fungi can cause seedlings to die while other soil fungi form beneficial symbiosis with seedlings that can help them thrive by obtaining key nutrients in the soil. The goal of this project is to better understand the contexts in which fungi promote seedling growth and maintain tree species diversity, in the context of a reforestation project. Degree of relatedness between adult trees will be a particular focus of this work, with the hypothesis that seedlings will interact with more beneficial fungi when they are planted near adult trees that are more genetically different from themselves. This project will take place in Ecuador, in a species-rich region that is increasingly threatened with deforestation, which releases carbon into the atmosphere. Reforestation, in contrast, creates a sink for carbon and habitat for many endangered species. This research on seedling-fungal interactions can aid in designing reforestation efforts. The broader impacts further include training a U.S. based post-doctoral associate and graduate student.This project provides a novel, multi-species test of the idea that, by selecting against more common genotypes and favoring survival of rarer genotypes, within-species specialization by pathogenic soil fungi promotes and maintains genetic diversity within plant species. At the same time, the research also explores whether and in what contexts soil fungal communities have positive impacts on seedlings. To do so, the team will implement a shade house experiment made possible by a large-scale reforestation project in Ecuador. The study design allows an assessment of seedling performance as a function of how related a given seedling’s maternal tree is to the conspecific tree in whose soil the seedling is planted. The design allows 36 within-species pairwise comparisons with 8 replicates each, for each of 16 different tree species, as well as controls with sterilized inoculum. Genetic relatedness of trees and profiles of fungal community composition and function will be assessed via high-throughput sequencing. This work is expected to provide novel data on the extent to which within-species specialization by soil fungi occurs; the degree to which genetic similarity between conspecific maternal trees predicts magnitude and direction of soil fungal impacts on seedling performance; and how specific combinations of soil and root fungal communities impact seedling performance. These findings are expected to advance our understanding of the ecological and microevolutionary factors that control the diversity of tropical treesThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.