Variation in ectomycorrhizal fungal communities associated with Oreomunnea mexicana (Juglandaceae) in a Neotropical montane forest.

Neotropical montane forests are often dominated by ectomycorrhizal (EM) tree species, yet the diversity of their EM fungal communities remains poorly explored. In lower montane forests in western Panama, the EM tree species Oreomunnea mexicana (Juglandaceae) forms locally dense populations in forest otherwise characterized by trees that form arbuscular mycorrhizal (AM) associations. The objective of this study was to compare the composition of EM fungal communities associated with Oreomunnea adults, saplings, and seedlings across sites differing in soil fertility and the amount and seasonality of rainfall. Analysis of fungal nrITS DNA (nuclear ribosomal internal transcribed spacers) revealed 115 EM fungi taxa from 234 EM root tips collected from adults, saplings, and seedlings in four sites. EM fungal communities were equally species-rich and diverse across Oreomunnea developmental stages and sites, regardless of soil conditions or rainfall patterns. However, ordination analysis revealed high compositional turnover between low and high fertility/rainfall sites located ca. 6 km apart. The EM fungal community was dominated by Russula (ca. 36 taxa). Cortinarius, represented by 14 species and previously reported to extract nitrogen from organic sources under low nitrogen availability, was found only in low fertility/high rainfall sites. Phylogenetic diversity analyses of Russula revealed greater evolutionary distance among taxa found on sites with contrasting fertility and rainfall than was expected by chance, suggesting that environmental differences among sites may be important in structuring EM fungal communities. More research is needed to evaluate whether EM fungal taxa associated with Oreomunnea form mycorrhizal networks that might account for local dominance of this tree species in otherwise diverse forest communities.