Environment is more important than ectomycorrhizal fungal identity in determining mycorrhizosphere enzyme activities

After clearcutting, there is typically a shift in ectomycorrhizal (ECM) fungal community structure and an increase in soil N availability. Many studies have morphologically and molecularly documented this shift in ECM fungal community structure, but none have investigated if a shift in ECM fungal community structure equates to a shift in community function. Extracellular enzyme activities (EAAs) are commonly investigated as a functional trait of interest as they comprise a major nutrient acquisition strategy of ECM fungi. Studies investigating EAAs of ECM root tips have indicated that ECM fungal identity can be more important that soil nutrient status in determining EEAs. However, in these studies, species differences were confounded with differences in environmental variables. In our experiment, a reciprocal transplant of one-year-old, naturally-regenerated subalpine fir (Abies lasiocarpa) seedlings was performed between three pairs of clearcut and adjacent forest plots. One growing season after transplantation, ECM fungal communities on seedlings originating from clearcuts and forests remained distinct in each destination environment. Relative growth and seedling survival rates did not differ between transplant treatments, but seedlings originating from clearcuts generally produced larger apical buds in both destination environments. The apical buds of these seedlings also had higher N contents than apical buds of seedlings originating from the forest. Activities of glucuronidase, xylosidase, cellobiohydrolase, β-glucosidase, N-acetylglucosaminidase, phosphomonoesterase, leucine aminopeptidase, and laccase were measured on individual mycorrhizal tips of transplanted seedlings. On non-metric multi-dimensional scaling ordinations, enzyme profiles of mycorrhizas clustered together based on destination environment within each clearcut/forest pair. No effect of source environment was apparent. However, a multi-response permutation procedure showed that enzyme activities differed both between destination environments as well as between source environments within destination environments. This strongly suggests that environment is the dominant determinant of EEAs, while fungal identity has a more minor influence on this functional trait. Hence, ECM fungal community function has the capacity to be resilient to ecosystem disturbances at high elevation subalpine sites in southern British Columbia.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat