Mycorrhizal guild functions and conservational values in boreal forests

Sammanfattning: The immense diversity and biomass of ericoid-, ectomycorrhizal, and saprotrophic fungal guilds in boreal forest soils make them vital components of conservation and ecosystem processes, and in particular, many ectomycorrhizal fungi are considered species of conservation concern. However, amalgamated information on the functions and relationships of soil fungi to perceived forest conservation values, and how inter and intra-guild interactions affect the accretion and decomposition of soil organic matter is lacking. In a long-term factorial shrub removal and pine root exclusion experiment, I assessed guild contributions to soil respiration and decomposition of organic substrates guided by ecological theory. Then in the northern and southern boreal forest, I evaluated whether forest conservation values are aligned with the diversity of ectomycorrhizal fungi. Overall, the ericoid guild makes a significant contribution to total soil respiration (11 ± 9%), and ericoid activities appeared to be more sensitive to periods of drought compared to ectomycorrhizal (43 ± 1%) and saprotrophic (53 ± 5%) guilds. Saprotrophic-ectomycorrhizal interactions during decomposition led to a modest, yet inconsistent Gadgil effect (10%) for early-stage litter decomposition. Ericoid and ectomycorrhizal guilds interactions were determined to be more important for late-stage organic matter balance in boreal forest soils. Ectomycorrhizal species richness was significantly higher in the southern boreal forest compared to the north. Furthermore, forest conservation values across the boreal forest were not adequately related to ectomycorrhizal diversity through DNA-metabarcoding. Instead, soil fertility, corresponding to tree species basal area, was the clearest indicator of ectomycorrhizal diversity and composition in both regions. Mycorrhizal guilds may be underappreciated and understudied in terms of conservation, but their functional roles in the accumulation and decomposition of organic matter in long-term soil carbon pools emphasizes the importance of evaluating the many dimensions of fungal conservation in boreal forests.