Adaptation mechanisms of the soil microbial community under nutrient-limited conditions in the dryland Mountains

Microbial nutrient limitation is crucial for shaping interspecific interactions and community assembly within soil microbial communities, and these processes are integral to understanding ecosystems response to global changes. However, whether and how nutrient limitation influences these processes in arid mountain ecosystems remains unclear. This study investigates the mechanisms of soil microbial community assembly along an elevational gradient in the Helan Mountains, a region characterized by significant environmental variation such as temperature, precipitation, and nutrient availability, using Illumina sequencing and extracellular enzymatic stoichiometry. Our results show that bacterial α-diversity and β-diversity declined with increasing elevation, whereas fungal α-diversity exhibited a hump-shaped, and fungal β-diversity showed a U-shaped pattern. Across all elevations, soil microorganisms were predominantly limited by carbon (C) and phosphorus (P), with P limitation intensifying at higher elevation, and C limitation peaking at mid-to-high elevations. Community assembly processes were dominated by stochastic processes bacterial community assembly at low and high elevations, whereas deterministic processes prevailed at mid-elevations for bacterial communities. In contrast, fungal community assembly was consistently governed by stochastic processes across the gradient. Network analysis revealed that the microbial communities at low to mid- elevations exhibited more cooperative interaction, with more stable bacterial and fungal networks. Partial least-squares path modeling further revealed that bacterial community assembly was primarily driven by microbial nutrient limitation and bacterial α-diversity, while fungal community assembly was directly influenced by nutrient limitation. This study provides new insights into soil microbial community assembly along elevation in arid mountain ecosystems and highlights how nutrient limitation dynamics and its driving forces vary with environmental gradient, offering valuable information for understanding ecosystem responses under global change.