COS 206-6 - Leaf traits correlate with species richness of foliar fungal endophytes - a continental and kingdom-wide study

Abstract: Foliar endophytes are one of the most diverse fungal guilds found in the photosynthetic tissues of every plant lineage. Despite major advances in sequencing technologies and rapid species identification, we still lack broad observational patterns from diverse hosts and ecosystems to formulate general hypotheses that explain what factors shape endophyte diversity. To address this gap, we sampled endophyte communities from 443 plant genera (n = 1,657 host individuals), spanning Bryophytes and Angiosperms. Leaf sampling from plant hosts took place across 20 sites from Panama to Alaska, covering a broad latitudinal gradient (9°N-64°N) in North America. We used ITS1 metabarcoding to characterize the fungal endophytes in mature leaves, resulting in a rarefied community dataset of 3500 reads per host. Our goal was to search for correlations between endophyte diversity and leaf functional traits that were available in the public databases of Glopnet (Global Plant Trait Network Database) and TRY. We explored correlations with the most commonly measured leaf traits, such as % nitrogen, % phosphorus, longevity, and toughness. Leaf trait values were averaged within plant genera. One of the most significant relationships found was a negative correlation between endophyte species richness and leaf nitrogen. This trend is consistent with the resource balance or competitive exclusion hypotheses, which rationalize that species will not exclude each other under nutrient limitation, allowing more species to coexist at low or intermediate nutrient levels. High nutrient levels may allow certain species to dominate the community, lowering total species richness. Leaf lifespan, which is negatively correlated with leaf N, was positively correlated with endophyte species richness. We discuss new hypotheses for how these correlations may depend on different regions (tropics vs. temperate forests) or can be informed by the leaf economics spectrum.