Variation regularity of stoichiometric characteristics of soil microbial biomass C, N, and P along the altitudinal gradient and their influencing factors in Helan Mountains

Soil microbial biomass, as the living organic matter portion of the soil, is an important ecological indicator of the flux and cycle of soil organic nutrient cycling. Investigating the vertical differentiation patterns and key influencing factors of the ecological stoichiometry characteristics of soil microbial biomass carbon (C), nitrogen (N), and Phosphorous (P) in arid and semi-arid mountainous ecosystems can provide references for understanding the processes and regulatory mechanisms of soil C, N, and P cycles in these ecosystems. This study focused on six typical zonal vegetation types at different altitudes in the Helan Mountains of Ningxia. We measured the soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). Using methods such as one-way analysis of variance, redundancy analysis, and variance partitioning analysis, the vertical differentiation characteristics of the ecological stoichiometry of soil microbial biomass C, N, and P and their relationships with climatic factors and soil physicochemical factors were analyzed. The results showed that the contents of soil microbial biomass C, N, and P varied significantly with altitude (P < 0.05). MBC and MBP showed a trend of first increasing and then decreasing with increasing altitude, while MBN increased with altitude. All three elements were highest in the subalpine shrub zone, with contents of 1 502.08, 35.42, and 127.55 mg·kg⁻¹, respectively. The ratios of MBC ꞉ MBP, MBN ꞉ MBP, and MBC ꞉ MBN fluctuated with altitude. MBC ꞉ MBP and MBN ꞉ MBP showed the highest values in the shallow mountain shrub zone. Redundancy analysis and variance partitioning analysis indicated that TN, mean annual temperature, pH, and TN ꞉ TP significantly affected the ecological stoichiometry characteristics of soil microbial biomass C, N, and P (P < 0.05). Soil physicochemical factors had a greater impact on the ecological stoichiometry characteristics of soil microbial biomass C, N, and P than did altitude and climatic factors. These results suggest that changes in soil physicochemical factors can significantly alter the ecological stoichiometry characteristics of soil microbial biomass C, N, and P.