Microbial specialists in high-altitude forest soils: environmental sensitivity and ecological significance

Microorganisms are essential contributors to the forest ecosystems of the Qinghai-Xizang Plateau, encompassing generalists, intermediates, and specialists. Investigating the characteristics and drivers of these microbial sub-communities across varying elevations is essential for understanding their ecological functions in high-altitude forest soils. This study examines the diversity patterns, assembly processes, environmental adaptations, and potential functions of bacterial and fungal sub-communities along an elevation gradient from 3900 m to the timberline on Shergyla Mountain, China. The findings revealed notable differences between low and high elevations in the diversity and composition of microbial sub-communities. According to neutral and null models, generalists, characterized by the widest niche width and highest migration rates, were primarily influenced by stochastic processes (71.9%). In contrast, deterministic factors, including homogeneous and variable selection, exerted a stronger effect on the assembly of specialists (51.0%). Elevation and nutrient availability emerged as key environmental drivers shaping microbial sub-communities, particularly for specialists, while generalists experienced fewer constraints from environmental factors. Network analysis further demonstrated that habitat specialists occupy central positions within microbial networks, playing a pivotal role in maintaining network stability. Additionally, nitrogen cycling genes—specifically nifH, amoA, nirS and nosZ—exhibited a U-shaped distribution across the elevation gradient and showed a substantial correlation (p < 0.05) with the Chao1 and Shannon indices of bacterial specialists. The results enhance our knowledge of microbial community dynamics and underscore the crucial ecological role of microbial specialists in the ecosystems of high-altitude forests.