Soil pH and moisture drive depth-specific patterns of SOC, TN, and TP along elevational gradients in Chinese montane forests.

Aims Elevational gradients have a strong influence on the spatial distribution of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). However, the depth-specific mechanisms driving these patterns remain insufficiently understood. This study aims to characterize the altitudinal distribution patterns of SOC, TN, and TP in surface and subsurface soils across mid-elevation mountain forests in China, explore the mechanistic roles of environmental drivers (e.g., pH, soil moisture) in regulating nutrient dynamics, and promote an understanding of C-N-P coupling in montane ecosystems. Methods By synthesizing literature-derived data from 137 mid-altitude transects spanning 22 mountain forest ranges across China, we quantify relationships of SOC, TN, and TP along mid-elevation gradients. Results SOC and TN concentrations exhibited significant positive correlations with elevation in topsoil and subsoil, with more pronounced accumulation trends in subsurface layers, as indicated by 36.84% of samples showing significant increases in SOC and TN concentrations. In contrast, TP displayed heterogeneous patterns, with only 11.1% of surface soils demonstrating significant declines. Our results specifically evaluated the effects of pH and soil moisture on nutrient dynamics across different soil depths, while quantifying the indirect influence of climate. Conclusions By clarifying depth-specific controls on nutrient patterns, our findings highlight the stability of C-N coupling and the central role of pH in stabilizing soil carbon in montane forests, offering theoretical insights for mountain forest management under elevational gradients.