DISSERTATION RESEARCH: Effects of nitrogen addition on ectomycorrhizal communities in tropical montane forest

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Tropical forests are renowned for their high biodiversity, with hundreds or even thousands of tree species living together at a single site. In some tropical forests, however, a single tree species can outnumber all other species combined. Recent attempts to explain this one-species dominance have focused on the role of soil microbes in determining which tree species are common and which are rare. Attention has been on beneficial associations between trees and fungi in their roots, called mycorrhizas. A leading idea about why some tropical trees are so common is that they are uniquely capable of forming associations with particular types of mycorrhizal fungi that provide access to nitrogen that is unavailable to less common tree species. Experimental work from a forest in western Panama is consistent with this hypothesis, leading to the question of how this plant-mycorrhizal association, and therefore tree community composition, may be disrupted by increasing rates of nitrogen deposition from the atmosphere. Will this new and relatively plentiful form of nitrogen make mycorrhizal fungi unimportant? Effects of nitrogen on the plant-mycorrhizal association of a dominant tree will be addressed by comparing mycorrhizal fungal communities in forest plots with and without a treatment of nitrogen fertilization over the last eight years. This project will also provide training in fungal genetics and ecology to a graduate student, and research mentoring for undergraduate students. The ectomycorrhizal fungal community associated with a dominant canopy tree, Oreomunnea mexicana, will be characterized in eight forest plots located in lower montane forest at Fortuna, Panama. Four of the plots have received a nitrogen addition treatment four times per year since 2008. In each plot, root samples will be collected from Oreomunnea trees and ectomycorrhizal communities characterized using Illumina sequencing. It is predicted that nitrogen addition will reduce the diversity and infection frequency of ectomycorrhizal taxa and result in a shift in the composition and phylogenetic structure of ectomycorrhizal communities, favoring lineages known to contain nitrophilic taxa.