Forest certification criteria often include a requirement that coarse woody debris (CWD) be retained on site after harvesting. However, we know little about how CWD influences soil biodiversity even though soil factors and associated ecosystem functions are always highly ranked in sustainability criteria. In this project we tested whether the retention of CWD influences taxonomic and functional biodiversity of the ectomycorrhizal fungal community at the plot scale in a sub-alpine clearcut. Three 10-ha cutblocks were harvested over the winter of 1994-95. Two 1-ha plots with either complete removal of CWD, or natural levels of CWD were established in each cutblock. Engelmann spruce seedlings were operationally planted in 1996. In September 2006, we harvested one long lateral root from 10 trees on each Complete Removal and Normal Level CWD plot. Then 100 randomly-selected ectomycorrhizas per root sample were carefully examined under dissecting and compound microscopes and separated into those colonized by different fungi. DNA was extracted from two mycorrhizas per morphotype per seedling and the fungal ITS region of nuclear rDNA amplified sequenced. In 2007, 21 mycorrhizal tips from each of the same seedlings were tested for the activities of seven extracellular enzymes using a microplate assay.
Results/Conclusions
A conservative analysis indicated no difference in species richness in the ectomycorrhizal fungal community between the plots differing in retention of CWD (9.8±0.8 genotypes per plot with no CWD and 11.0±16.7 genotypes with normal retention). However, DNA from the saprotroph Alloclavaria purpurea was amplified from multiple mycorrhizas from morphotypes representing 50% of the roots, leaving the status of these data points in doubt. Cloning analyses of these samples should resolve whether A. purpurea colonizes roots in this system, or whether it is a frequent rhizosphere associate. The levels of CWD at the plot level weakly affected the activities of some extracellular enzymes in the mycorrhizospheres. Activities of xylosidase,(P = 0.12) and cellobiohydrolase (P=0.07) tended to be lower and acid phosphatase activities (P=0.10) tended to be higher in plots without CWD Differences amongst the three cutblocks were much greater than treatment effects. Given that sampling was not targeted relative to the pieces of CWD, it is not surprising that differences in the ectomycorrhizal fungal community were minor. Still, this study provides some indication that retention of coarse woody debris may encourage a more physiologically diverse ectomycorrhizal fungal community.
