Below-ground ectomycorrhizal community structure in a recently burned bishop pine forest

1 The effects of wildfire ash on ectomycorrhizal (EM) associations were investigated by sampling bishop pine (Pinus muricata, D. Don) seedlings from control and ash-removed plots 1.5 years after a severe lire in a northern Californian P. muricata forest. The below-ground community composition of EM at the site was characterized using molecular techniques (PCR-RFLP and nucleotide sequencing). 2 A total of 30 fungal taxa were observed, many of which differed in their distribution between treatment and control seedlings. However, most of the taxa that were distinctive to either treatment or control seedlings occurred only once across the site, precluding statistical detection of potential ash effects on EM community composition. There were no significant effects of ash removal on plot-level mycorrhizal community richness or diversity, and there were no distinct treatment-related clusters in a principal components analysis. 3 Analysis of the combined data indicated that numbers of fungal taxa per seedling, numbers of successive root depth increments colonized by the same taxon, and distances to neighbouring seedlings colonized by the same taxon, were randomly distributed across the site for the majority of mycorrhizal fungi. These distributional patterns suggest that the post-fire mycorrhizal community structure on P. muricata arose primarily from successful colonization by randomly distributed point-source fungal inocula within the upper mineral soil layer of the forest floor. 4 By comparison with pre-fire studies from similar P. muricata sites nearby, our data indicate that severe wildfire disturbance resulted in marked changes in mycorrhizal community composition, and a sharp increase in the relative biomass of ascomycetous fungi.