Ectomycorrhizal (ECM) root tip community structure and enzyme activity varies between forest and clearcut plots, and there is evidence of functional complementarity among dominant ECM taxa in forest plots

Background/Question/Methods

Ectomycorrhizal fungi (EMF) that colonize seedlings in forests are different from those in clearcuts, possibly because of limited inoculum and altered abiotic properties. Downed logs influence the environment for EMF, and decayed downed wood is penetrated by the roots of tree seedlings and their EMF symbionts. By increasing habitat diversity, and acting as a potential source of inoculum, downed wood may be important for preserving forest EMF species in disturbed stands. The study of enzyme profiles associated with EMF provides information on the functional diversity of an EMF community. This knowledge is valuable for forest management if the loss of EMF taxa results in decreased fitness for regenerating seedlings due to diminished EMF community physiological function. We identified the fungal symbiont and quantified the exoenzyme activity of ectomycorrhizae on spruce seedlings planted in a high elevation forest and in adjacent clearcut plots from which downed wood generated during harvesting was either removed or retained. Our objective was (i) to determine if there were differences in EMF community structure and physiological activity between clearcut and forest plots, and (ii) to explore the capacity of dominant EMF taxa for plasticity among plots, and/or functional complementarity among EMF species in the same plot.

Results/Conclusions

We detected 44 EMF taxa, and 15 taxa suspected of forming mycorrhizal associations. Amphinema byssoides, Thelephora terrestris, and Tylospora spp. made up the largest proportion of identified mycobionts. Forest plots had higher EMF taxon richness and a distinct EMF community compared to clearcut plots. Total C and N, available phosphate-P and nitrate-N, and mineralizeable-N were highest in forest plots, where soil temperature and pH were lowest. EMF community laccase and phosphatase activities were highest in forest soils, yet we did not detect physiological plasticity among plots for any of the dominant EMF taxa. Dominant EMF taxa appeared to have complementary enzyme profiles in the forest plots. We could not determine if ecosystem function was maintained in clearcuts, in part because of the overall dominance of most of the enzyme profile by T. terrestris. We were able to show that downed wood retained on clearcut blocks provided potential habitat for forest EMF by creating abiotic conditions similar to forest soils, but this did not result in EMF community structure or function resembling that of the original forest. We conclude that retention of wood on clearcut blocks should continue, if only to provide diverse habitat for regenerating seedlings and their EMF symbionts.