Soil fungi play an integral and essential role in maintaining soil ecosystem functions. The understanding of altitude variations and their drivers of soil fungal community composition and diversity remains relatively unclear. Mountains provide an open, natural platform for studying how the soil fungal community responds to climatic variability at a short altitude distance. Using the Illumina MiSeq high-throughput sequencing technique, we examined soil fungal community composition and diversity among seven vegetation types (dry valley shrub, valley-mountain ecotone broadleaved mixed forest, subalpine broadleaved mixed forest, subalpine coniferous-broadleaved mixed forest, subalpine coniferous forest, alpine shrub meadow, alpine meadow) along a 2582 m altitude gradient in the alpine–gorge region on the eastern Qinghai–Tibetan Plateau. Ascomycota (47.72%), Basidiomycota (36.58%), and Mortierellomycota (12.14%) were the top three soil fungal dominant phyla in all samples. Soil fungal community composition differed significantly among the seven vegetation types along altitude gradients. The α-diversity of soil total fungi and symbiotic fungi had a distinct hollow pattern, while saprophytic fungi and pathogenic fungi showed no obvious pattern along altitude gradients. The β-diversity of soil total fungi, symbiotic fungi, saprophytic fungi, and pathogenic fungi was derived mainly from species turnover processes and exhibited a significant altitude distance-decay pattern. Soil properties explained 31.27−34.91% of variation in soil fungal (total and trophic modes) community composition along altitude gradients, and the effects of soil nutrients on fungal community composition varied by trophic modes. Soil pH was the main factor affecting α-diversity of soil fungi along altitude gradients. The β-diversity and turnover components of soil total fungi and saprophytic fungi were affected by soil properties and geographic distance, while those of symbiotic fungi and pathogenic fungi were affected only by soil properties. This study deepens our knowledge regarding altitude variations and their drivers of soil fungal community composition and diversity, and confirms that the effects of soil properties on soil fungal community composition and diversity vary by trophic modes along altitude gradients in the alpine–gorge region.

The land-use change is a major determinant influencing ecosystem carbon (C) patterns and nutrient cycling in subalpine forests in the Eastern Tibetan Plateau. While some results have been obtained in relation to the influence of land-use change on aboveground components, less is known about the belowground microbial communities and related processes. We assessed the structure and function of soil microbial communities following land-use change from old-growth forest (OF) to secondary forest (SF), plantation forest (PF), and grassland (GL) in the Eastern Tibetan Plateau, China. Phospholipid fatty acid profiles and enzyme activity analysis were used to determine the composition and activities of microbial communities, respectively. Significant differences in physicochemical characteristics, microbial communities, and extracellular enzyme activities in soils under different land uses were observed in this study. pH and total nitrogen (TN) in OF and SF were significantly higher than in GL. PF showed the highest soil organic C (SOC), and significantly higher than in GL. Total phosphorus (TP) and C/N ratio in PF were significantly higher than the other land-use types. OF and PF had significantly higher anaerobic bacteria than in GL. The actinobacteria in SF was significantly higher than in PF. The saprotrophic and ectomycorrhizal (SEM) fungi was significantly lower in GL than the other land-use types. Total microbial biomass and β-glucosidase activities were significantly higher in OF and SF than in GL. GL had significantly higher polyphenoloxidase activities than in OF and PF. Anaerobic bacteria, arbuscular mycorrhizal fungi and SEM fungi were positively correlated with SOC and TP, Gram+ bacteria were correlated with C/P and N/P ratio. N-acetylglucosaminidase activity was negatively correlated with anaerobic bacteria, while polyphenoloxidase activity was positively related to actinobacteria. Furthermore, redundancy analysis revealed that the microbial community composition was primarily regulated by TN and pH. This suggested that altered land-use type initiated changes in the physicochemical characteristics of the soils, which affected the composition of microbial communities and microbial enzyme activities related to nutrient cycling in this area. This provides a scientific basis for the influence mechanism of land use on composition and function of microbial communities, as well as the rational utilization and management of land resources.

Fine roots play a crucial role in plant survival potential and biogeochemical cycles of forest ecosystems. Subalpine areas of the Eastern Qinghai-Tibetan Plateau have experienced different forest re-establishment methods after clear-cutting primary forest. However, little is known about fine root dynamics of these forests originating from artificial, natural and their combined processes. Here, we determined fine root traits (biomass, production and turnover rate) of three subalpine forest types, i.e., Picea asperata Mast. plantation forest (artificial planting, PF), natural secondary forest (natural without assisted regeneration, NF) and P. asperata broadleaved mixed forest (natural regeneration after artificial planting, MF) composed of planted P. asperata and naturally regenerated native broadleaved species. At the soil depth of 0–30 cm, fine root biomass was the highest in PF and fine root production was the highest in NF, and both were the lowest in MF. Fine root dynamics of the three forest types tended to decrease with soil depth, with larger variations in PF. Fine root biomass and production were the highest in PF in 0–10 cm soil layer but were not significantly different among forest types in the lower soil layers. There were positive correlations between these parameters and aboveground biomass across forest types in soil layer of 0–10 cm, but not in the lower soil layers. Fine root turnover rate was generally higher in mixed forests than in monocultures at all soil depths. In conclusion, the natural regeneration procedure after clear-cutting in the subalpine region of western Sichuan seems to be superior from the perspective of fine root dynamics.

Soil fungi play an indispensable role in maintaining soil ecosystem functions. However, how forest succession and soil depth interactively shape fungal community composition and diversity remains poorly understood. To address this, we investigated fungal communities across four successional stages and two soil depths (0–10 cm and 40–60 cm) in a subalpine forest on the eastern Qinghai–Tibetan Plateau using Illumina high-throughput sequencing. Results showed that the soil fungal community composition of different trophic modes varied significantly with both succession and soil depth. The α-diversity of symbiotic and saprotrophic fungi responded to succession in a depth-dependent manner, while β-diversity across all trophic modes was primarily driven by species turnover. Soil properties and vegetation factors collectively explained 69.85–82.91% of the variation in soil fungal community composition, with their effects being dependent on both soil depth and trophic mode. Specifically, in topsoil, the β-diversity of symbiotic fungi was influenced only by soil property heterogeneity, whereas that of saprotrophic and pathogenic fungi was shaped by both vegetation and soil property heterogeneity. In subsoil, symbiotic fungal β-diversity was co-regulated by vegetation and soil properties heterogeneity, while saprotrophic fungal β-diversity was driven solely by soil properties heterogeneity. This study demonstrates that soil depth modulates the successional dynamics of soil fungal communities and highlights the trophic-dependent drivers of fungal assembly in forest soils.