Changes in vegetation type shape the soil microenvironment, thereby regulating the changes in the organic carbon pool by influencing microbial communities and the accumulation of microbial necromass carbon (MNC). This study investigated microbial biomass—via phospholipid fatty acids (PLFAs) analysis—and MNC accumulation across three cold–temperate forest types: Larix gmelinii forest (L), Larix gmelinii–Betula platyphylla Sukaczev mixed forest (LB), and Betula platyphylla Sukaczev forest (B). The results showed that the L had the lowest contents of pH, water content (WC), soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), and total phosphorus (TP), but the highest contents of dissolved organic carbon (DOC), available phosphorus (AP), and carbon to nitrogen ratio (C/N) (p < 0.05). LB had the lowest PLFAs content and the highest ratio of Gram-positive bacteria/Gram-negative bacteria (G+/G−), and total fungi/total bacteriai (F/B) of L was the highest. B had the highest alpha diversity index, and significantly positively correlated with pH, SOC, TN, AN, and TP. TP and C/N were the primary elements for significant differences in microbial community structure. The order of MNC content and its contribution to SOC was B > LB > L. MNC was significantly negatively correlated with PLFAs, DOC, and AP, and significantly positively correlated with pH, SOC, TN, AN, TP, Shannon–Wiener and Pielou indices. In conclusion, this study demonstrates that Betula platyphylla Sukaczev forest retains more carbon, nitrogen, and phosphorus, microbial alpha diversity, and acquires more MNC, which can provide a basis for subsequent forest management and carbon sequestration projects.

The genera Cortinarius and Russula are common ectomycorrhizal fungi, serving as excellent indicators of forest ecosystem health and soil conditions. This study conducted a systematic taxonomic investigation of macrofungi in the Huzhong National Nature Reserve of the Greater Khingan Mountains, integrating morphological and molecular phylogenetic analyses. Six new record species for China were identified: Cortinarius acutus, Phlegmacium balteatum, Cortinarius huronensis, Cortinarius lewisii, Cortinarius luteoornatus, and Russula grisescens. The article provides descriptions of their morphological characteristics and distribution, supported by phylogenetic analysis using ITS sequences. These findings expand the known distribution of these taxa to China’s taiga forests, reveal the region’s rich macrofungal diversity, and provide essential data for taxonomic, biogeographic, and forest ecosystem research.

Forest fires are key disturbance factors in forest ecosystems, and soil fungi play an irreplaceable role in post-fire recovery. This study focused on forest areas burned in 2000 in the Daxing’anling region of China, targeting long-term recovery sites with different fire intensities. Illumina MiSeq sequencing was used to analyze the structural characteristics of fungal communities and their environmental drivers. Results showed that compared with the control check (CK), the Shannon index of the low fire group (L) increased significantly (p < 0.05), while moderate (M) and high (H) fire groups reduced fungal diversity significantly. PCoA indicated significant differences in community structure (R² = 0.97, p = 0.001). In highly burned areas, the relative abundance of Ascomycota reached 94.17%, and Basidiomycota lost its dominance. Spearman analysis showed that pH, available phosphorus, available potassium, soil fluorescein diacetate hydrolase, soil dehydrogenase, and soil urease were significantly positively correlated with fungal alpha diversity. RDA revealed that total nitrogen, available phosphorus, soil water content, alkaline nitrogen, active potassium, and dissolved organic carbon had extremely significant effects on soil fungal community composition (p < 0.01). Co-occurrence network analysis indicated that symbiotic relationships dominated all groups. Networks in L and M groups were more complex, while that in H group was simplified and severely damaged. This study indicated that after long-term recovery, soil fungal communities in low fire areas returned to pre-fire levels; those in moderate and high fire areas did not recover, with high fire burns causing severe damage and community structure reorganization.

Permafrost regions serve as sensitive indicators of global warming due to their ecological sensitivity and role as climate archives. To study how soil microbial communities in seasonal permafrost respond to freeze–thaw alternations, we analyzed composition and diversity during freezing, freeze–thaw, and thawing stages, identifying key taxa and environmental drivers. Our results identified 11 known fungal phyla and 13 dominant genera in permafrost regions. Most dominant fungi showed stable abundance during soil warming. However, the genera Inocybe and Sebacina were significantly suppressed when transitioning from frozen to freeze–thaw conditions. Fungal species diversity gradually increased with rising temperature and freeze–thaw frequency, with thawed soil showing higher richness and evenness. Frozen, freeze–thaw, and thawed soil were respectively associated with 90.48%, 71.43%, and 66.67% of node species. Adjacent stages shared 57.14% of coexisting species. Keystone node species declined progressively from frozen to thawed stages, indicating substantial yet continuous community reorganization. Furthermore, total carbon, organic carbon, available nitrogen, and phospholipid fatty acids peaked in freeze–thaw alternating soil. Active fungal biomass and species richness were most strongly correlated with soil carbon, temperature, and moisture. Overall, the influence of nutrients on soil fungi was limited across different freeze–thaw stages, while temperature emerged as the primary driver reshaping fungal community structure during freeze–thaw dynamics.

Heterotrophic microorganisms derive energy by decomposing organic matter. Their composition and community structure are influenced by environmental factors and interactions. Soil heterotrophic respiration was assessed by establishing vegetation removal plots (Hr) and control plots (Sr). Soil physicochemical properties were analyzed, and the composition and biomass were evaluated using Illumina HiSeq sequencing and PLFA. The pH of Hr exhibited a significant increase (p < 0.05), whereas MC, MBC, SOC, DOC, TN, and AN all showed significant decreases (p < 0.05). PLFA analysis revealed that the biomass of bacteria, fungi, and total microorganisms in Hr was significantly lower than in Sr (p < 0.05). The predominant bacterial phyla were Acidobacteria, Verrucomycota, and Proteobacteria, with Verrucomycota significantly more abundant in Hr. The dominant fungal phyla were Ascomycota and Basidiomycota, both significantly more abundant in Hr. Community assembly was governed primarily by homogeneous selection in both Hr and Sr. The Hr co-occurrence network showed higher complexity, with >60% positive associations. Mantel tests confirmed significant links between soil properties (MC, pH, MBC, SOC, DOC, TN, and AN) and microbial composition. Vegetation removal induced soil heterogeneity and reduced microbial biomass with specific taxa shifts (Verrucomicrobia, Ascomycota, and Basidiomycota). Altered soil conditions and carbon resources reorganize microbial structure and function.