Ectomycorrhizal Community Change along a Post-Wildfire Chronosequence of Michigan Jack Pine Stands.

Studies of successional changes in forest community composition have almost exclusively focused on aboveground biota; yet, we increasingly realize that above- and belowground communities are intimately linked.  We investigated changes in the community composition of ectomycorrhizal fungi (EMF) along a six-site chronosequence of jack-pine dominated stands (5, 11, 19, 23, 47 and 56 y post-wildfire). We collected 20 soil cores every 5 m along 4 100-m transects, for a total of 80 samples per site.  In each sample, a mycorrhizal root-tip was randomly selected; the fungal isolate was identified by extracting, amplifying and sequencing the internal transcribed spacer (ITS) regions of the rDNA, followed by a BLAST search in GenBank.  Sequences were edited with SeqMan 7.0 and aligned with ClustalW in MEGA 4.0; all isolates with 97% base-pair homology were grouped within the same taxonomic unit.  We compared both EMF community diversity and composition between sites using the Simpson's diversity index, average-linkage clustering analysis (ALCA) and principal components analysis (PCA) in R 2.6.1.  Overall, we observed little difference in diversity, yet a shift in community composition between the young and mid-to-older aged sites.  The two youngest sites grouped together in the ALCA, and merged last with the other sites.  Likewise, in the PCA, the two youngest sites separated from the other sites along PC 1, which accounted for 46% of the variation in the data.  Rhizopogon and Thelephora taxa, more prevalent in the younger sites, had high negative PC 1 loadings (-0.96 and -0.95, respectively), whereas Cortinarius and Russula taxa had high positive loadings.  Our findings suggest that a shift occurs in the EMF community within the first 20 y of stand development in these jack pine forests; whereas, following this time period, the community remains relatively similar in composition.