Phylogenetic structure of ectomycorrhizal fungal communities of western hemlock changes with forest age and stand type.

On Vancouver Island, British Columbia, fertilization with nitrogen (N) and phosphorus (P) following clearcutting increases growth of western hemlock. To explore whether fertilization also resulted in ectomycorrhizal fungal communities that were more or less similar to neighboring unlogged stands, we sampled roots from western hemlock from three replicate plots from each of five different, well-characterized, forest stand types that differed in site type, and in logging and fertilization history. We harvested four samples of 100 ectomycorrhizal root tips from each plot, a total of 60 samples per stand type. From each sample, we analyzed fungal ribosomal internal transcribed spacers and 28S DNA, sequencing 15-29 clones per sample and 60-116 clones per plot. We detected 147 fungal operational taxonomic units among a total of 1435 sequences. Craterellus tubaeformis was frequently present and resulted in a pattern of phylogenetic overdispersion in the fungal communities. Fungal species composition was strongly correlated with foliar nitrogen concentration. However, other site quality factors were also important because the fertilized regenerating hemlock and mature hemlock-amabilis fir forests had similar foliar nitrogen content but little overlap in fungal species. Compared with unfertilized regenerating forests, fungal communities in N + P-fertilized regenerating forests had significantly more species overlap with old growth forests. However, the fungal communities of all regenerating forest were similar to one another and all differed significantly from older forests. By correlating fungal clades with habitats, this research improves understanding of how forest management can contribute to maintaining diverse ectomycorrhizal fungal communities across a landscape.