A molecular and phylogenetic analysis of the structure and specificity of Alnus rubra ectomycorrhizal assemblages

Ectomycorrhizal (EM) assemblages associated with Alnus spp. are often distinct in composition and richness from other host plants. To examine the EM assemblage associated with A. rubra, a common tree in western coastal North America, we sampled four A. rubra forests varying in age, management history, and geographic location in Oregon, USA. From the 364 EM root tip rDNA ITS sequences, we found a total of 14 EM taxa. The five most abundant taxa, Tomentella sp. 3, Alnicola escharoides, Tomentella sp. 1, Lactarius cf. obscuratus, and Alpova diplophloeus, represented 80 % of the samples and were present at all four sites. Assemblage structure differed significantly among young managed sites and older unmanaged sites but not by geographic location. The younger managed sites had higher tree density, Frankia frequency, and soil nitrogen than older unmanaged sites. Phylogenetic analyses revealed that Alnus-associated EM congeners were not closely related, indicating the distinct nature of Alnus EM assemblages is not due to a unique co-evolutionary history.