Ectomycorrhizal community composition and structure of a mature red alder (Alnus rubra) stand

Regional and global studies of ectomycorrhizal fungal (EMF) communities associated with Alnus have made progress in determining the key factors that influence EMF diversity and biogeography. Smaller scale studies provide a valuable complement by relating EMF to environmental gradients and describing how community composition is influenced by competition and niche partitioning. We examined controls on EMF community composition in an 80 y-old Alnus rubra stand. EMF species were identified using root tip morphology and DNA sequencing, and related to soil variables (soil moisture, total C, total N, C:N ratio, PO4-P, soil pH) and to Frankia nodulation using Threshold Indicator Taxa ANalysis (TITAN) and multivariate techniques. Twenty-two EMF species were identified, including 14 that are new associates of A. rubra. EMF community composition varied temporally and was influenced by Frankia nodulation and soil chemistry. Species co-occurrence patterns suggest niche partitioning and competitive exclusion interact with subtle differences in the soil environment to influence EMF community composition.