Microorganisms play a key role in soil carbon (C) storage processes, with potential implications on the ability of managed boreal forests to store C and contribute to climate change mitigation. However, the taxonomic groups and microbial functions involved in these processes, and how they are affected by forestry practices, remain poorly understood. The aim of this study was to evaluate how forest harvesting shapes soil microbial communities and to elucidate the mechanisms through which ectomycorrhizal fungi (EMF) and ericoid mycorrhizal fungi (ErMF) are associated with soil C storage. We compared soil bacterial and fungal communities of clearcut and partial cut stands to those of unharvested stands of upland boreal balsam fir forests of eastern Canada using DNA metabarcoding. Path analysis and structural equation modelling were used to examine relationships among functional mycorrhizal groups, soil C stocks, and physicochemical properties. Results showed that clearcutting and partial cutting generally did not affect bacterial communities relative to control stands, but that clearcutting had significant effects on the diversity and composition of fungal communities compared to control stands. Although the effects diminished with soil depth, the most significant impact of clearcutting was a decrease in EMF relative abundance down to 55 cm in the mineral horizons. In soil surface organic horizons, the relative abundance of EMF with melanized hyphae, which are poorly degradable and can form complexes with metal ions, was positively associated with C stocks through pathways consistent with reduced oxidative decomposition, whereas the relative abundance of EMF with Mn-peroxidase capacity was negatively associated with C stocks. In the top 35 cm of mineral soil, ErMF relative abundance was linked to C storage through distinct pathways, including positive associations with mineral-associated organic matter C stocks mediated by pyrophosphate-extractable Fe and Al and C-to-nitrogen ratio, and direct associations with particulate organic matter C stocks. These findings improve our understanding of the fungal mechanisms underlying soil C storage and may help inform forest management strategies aimed at maintaining soil C stocks.
Climate change is intensifying drought frequency, threatening forest ecosystem stability. Soil fungal communities, critical for ecosystem carbon and nutrient cycling, exhibit complex responses to environmental stress, yet the interplay between community composition, activity, and forest type remains poorly understood. Here, we investigated seasonal drought with additional rain exclusion and recovery dynamics of soil fungi in pure European beech (Fagus sylvatica) [B], pure Douglas fir (Pseudotsuga menziesii) [D] forests and their mixtures [DxB] across a cool-humid and a warm-dry region. Using DNA- and RNA-based ITS sequencing, we distinguished total (DNA-based) and active (RNA-based) fungal communities, alongside soil moisture, soil properties, and microbial biomass. Microbial biomass decreased with decreasing soil moisture, irrespective of region and stand type, whereas no such relationship was observed for fungal richness. Total fungal communities remained stable across time and treatments, presenting a persistent fingerprint of long-term site conditions shaped by climate, soil properties, and forest type. In contrast, active fungal communities showed pronounced temporal dynamics, but exclusively in monocultures in the cool-humid region. The shifts in fungal community structures were driven by forest type and temperature, rather than low soil moisture. Prolonged stress over the summer induced transient increases of mycorrhizal, saprotrophic and multi-guild taxa with near-complete recovery of mycorrhiza taxa toward late fall, supporting high resilience of this guild in pure beech stands. Conversely, active fungal taxa in Douglas fir forests declined and showed only partial recovery. Mixed forests exhibited minimal changes, highlighting their stabilizing role. In the warm-dry region, active communities remained unchanged, suggesting stress-adapted fungal communities. These findings demonstrate that the interplay of forest composition, climate and season governs fungal resilience. Our results underscore the importance of distinguishing total and active communities in assessing climate resilience and highlight mixed-species forestry as a key strategy for maintaining soil microbial stability and ecosystem function under climate change.
Peatland forests provide major carbon storage and water regulation functions in the boreal zone, and they are heavily affected by management and tree harvesting. Peatland soils exhibit distinct physical, chemical and biological properties, which may lead to microbial responses differing from those observed in mineral upland forests. Here, we evaluated how this specific ecosystem responds to selection cutting (thinning) and clearcutting over a 30-month period following harvesting. Soil physicochemical properties, plant, and microbial communities were assessed in clearcut, selection-harvested and non-harvested control area in a drained peatland forest in southern Finland. Soil C was not significantly affected by forest management, whereas harvesting influenced N and P contents in the harvested areas at six months only. In contrast, water table depth rose significantly in both the clearcut and thinned areas throughout the study period. The plant root community responded rapidly, with clearcutting leading to a sharp reduction in the share of trees and their replacement by herbaceous and shrub species. These vegetation and environmental changes were accompanied by pronounced shifts in soil microbial communities. From six to 30 months, the relative abundance of ectomycorrhizal (EcM) fungi strongly declined after clearcutting, while the relative abundance of saprotrophic fungi increased at 18 months only, indicating a functional reorganisation of fungal assemblages. Total PLFA concentration increased significantly in the clearcut area at 18 and 30 months, and more transiently in the thinned area. No significant treatment effect was detected on fungal PLFA or the F/B ratio. The total fungal community showed no significant difference in multivariate dispersion. In contrast, bacterial assemblages showed greater multivariate dispersion in the clearcut area, indicating increased community heterogeneity. Vegetation composition and soil chemistry covaried with fungal communities, with carbon content and phosphorus among the associated variables. Overall, the rapid decline in the relative abundance of EcM fungi and their replacement by saprotrophs following harvesting indicates a potential shift in fungal decomposition pathways. This community shift may potentially impact carbon and nutrient cycling and forest regeneration.
Excessive atmospheric nitrogen (N) deposition has profoundly altered nutrient dynamics in plant-soil systems, significantly influencing phosphorus (P) cycling in forest ecosystems. Here, we explore the mechanisms driving soil P mobilization under N enrichment in N-limited but P-rich subalpine forests that are highly sensitive to N deposition. We experimentally manipulated both the duration and rate of N addition in a P-rich subalpine forest on the eastern Tibetan Plateau. We evaluated shifts in soil P availability across diverse P pools and elucidated the roles of roots and fungal hyphae in mediating P transformation using ingrowth cores with three mesh sizes. Intensified N addition altered N-P stoichiometry within the plant-soil system, triggering microbial C and P limitation in the root-mediated systems (2-mm cores). Irrespective of initial soil P availability, bioavailable P responses to sustained N enrichment were consistently negative in root-mediated systems, driven by microbial community restructuring and enzyme-mediated organic P mineralization. The depletion of bioavailable P was mechanistically attributable to a transition from root-based P acquisition toward increased reliance on hyphal outsourcing under increasing N loadings, thereby promoting root P uptake and microbial carbon and P assimilation. Our findings demonstrate that atmospheric N deposition accelerates soil P turnover in P-rich subalpine forests and highlight a shift toward hyphae-associated pathway to soil P dynamics amid emerging microbial P limitation, advancing understanding of nutrient interactions and plant-microbe acclimation mechanisms under global change.
