Species diversity of fungal endophytes across a stress gradient for plants

Foliar fungal endophytes are one of the most diverse guilds of symbiotic
fungi found in the photosynthetic tissues of every plant lineage, but it
is unclear how plant environments and leaf resource availability shape
their diversity. We explored correlations between leaf nutrient
availability and endophyte diversity among Pinus
muricata and Vaccinium ovatum plants growing
across a soil nutrient gradient spanning a series of coastal terraces in
Mendocino, California. Endophyte richness decreased in plants with higher
leaf nitrogen‐to‐phosphorus ratios for both host species, but increased
with sodium, which may be toxic to fungi at high concentrations. Isolation
frequency, a proxy of fungal biomass, was not significantly predicted by
any of the same leaf constituents in the two plant species. We propose
that stressed plants can exhibit both low foliar nutrients or high levels
of toxic compounds, and that both of these stress responses predict
endophyte species richness. Stressful conditions that limit growth of
fungi may increase their diversity due to the suppression of otherwise
dominating species. Differences between the host species in their
endophyte communities may be explained by host specificity, leaf
phenology, or microclimates.