Mycorrhizal dominance of the boreal forest soil community

Fungi are key players in nutrient cycling in the boreal forest, yet their diversity and specific roles are completely undescribed. Boreal forest soils contain roughly one quarter of Earth's labile organic carbon, but changes in climate and disturbance regimes are likely to substantially alter northern carbon dynamics. We are characterizing fungal community structure across habitats, successional stages, and soil horizons, primarily within the Bonanza Creek LTER site of interior Alaska. Here we present analyses of fungal communities from a single black spruce stand. Litter, humic, and mineral horizons were subsampled from 96 soil cores and community DNA was isolated from each subsample. The ITS + partial LSU rRNA region was amplified from each DNA extract and amplicons were then pooled by horizon. Three clone libraries were constructed: one for the litter layer (Lucigen, low bias system) and two for the humic layer (Invitrogen and Lucigen). OTUs at 97% identity were subjected to BLAST and MEGAN taxonomic parsing, then analyzed by calculating diversity and similarity indices with EstimateS, and performing phylogenetic comparisons with UniFrac. Comparisons of the three libraries revealed no phylogenetic difference between Lucigen and Invitrogen libraries, but significant differences in phylogenetic constituency of the litter and humic libraries. Across all clones 1) Mycorrhizal taxa were dominant; definitively saprophytic taxa were rare (<10%), 2) ECM fungi comprised nearly half of all sequences, and ericoid taxa were also abundant, 3) With the exception of Cortinarius, abundant aboveground fruiters were not dominant belowground, 4) Half of ECM sequences belonged to the resupinate taxa Piloderma and Amphinema, which may mobilize nutrients from organic substrates, 5) Several strikingly novel lineages were recovered, 6) Hundreds of taxa were found representing all four fungal phyla and numerous orders, and 7) This stand was undersampled, as taxon accumulation curves showed no inflexion toward an asymptote.