Coarse woody debris retention in subalpine clearcuts affects ectomycorrhizal root tip community structure within fifteen years of harvest

Shifts in ectomycorrhizal (ECM) fungal community composition occur after clearcut logging, resulting in the loss of some dominant forest fungi. Because decaying wood is a remnant of the original forest and an important habitat for ECM fungal species, we examined ECM spruce roots and hyphae in 1-ha coarse woody debris (CWD) retention and removal plots (N= 3) at a high elevation spruce forest 12 and 13 years after clearcut harvesting to test for a medium-term effect of CWD retention. Root tips from ten Picea engelmannii (Parry ex. Engelm.) saplings per plot were grouped morphologically, and the ECM fungal symbiont identified by Sanger sequencing. Sand-filled hyphae-trapping mesh bags were buried amongst the roots of saplings for one year. PCR product from all bags per plot was pooled and submitted for GS-FLX Titanium sequencing. Forty-six of 89 operational taxonomic units (OTUs) from root tips and 50 OTUs from hyphae were identified as ECM taxa. The most abundant taxa amongst root tip OTUs were Thelephora terrestris, Alloclavaria purpurea, Amphinema byssoides, and Tylospora asterophora. The most abundant OTUs from mesh bags were ectomycorrhizal taxa, and the most abundant of these were A. byssoides, T. terrestris, Wilcoxina mikolae, and T. asterophora. The retention of CWD had no detectable effect on taxon richness, evenness or diversity of ECM fungi on root tips or in mesh bags; however, there was a detectable shift in species composition. The relative abundance of A. byssoides root tips was significantly higher at removal plots while A. purpurea was a significant indicator species for CWD removal. Our results suggest that the retention of CWD at the time of harvest has affected ECM habitat at this site, and has resulted in altered ECM species composition, even though the logs are still hard and intact.