Patterns of Soil Carbon, Nitrogen and Phosphorus Stoichiometry in Baishanzu Mountain and Their Response to Altitude

This study aims to explore the response of soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometric characteristics at different altitudes in Baishanzu Mountain, and provide a foundation for identifying soil nutrient limitation in subtropical mountain ecosystems and uncovering the mechanisms of soil C, N, and P cycling. Plots were set at four altitudinal gradients (700–900 m, 1100–1300 m, 1300–1500 m, and 1500–1700 m) in Baishanzu Mountain, and soil organic C, total N, total P contents, their stoichiometric ratios were measured by analyzing soil samples collected and environmental factors. The relationship between soil properties and environmental factors was explored by using correlation and regression analysis method. The contents of soil C and N increased significantly with the elevation of altitude (P<0.05), the content of soil C reaching a maximum (85.16 g·kg^–1) at 1300-1500 m altitude, the content of soil N mounting to a maximum (5.65 g·kg^–1) at 1500−1700 m altitude, the content of soil P having no significant change. The variation of soil C and N content under different altitude gradients was highly coupled (R²=0.86, P<0.01), while P content and C and N content showed uncoupled characteristics. The ratios of soil C∶N, C∶P and N∶P all increased first and then decreased with the altitude upgrading, the highest value of which appeared at 1300–1500 m altitude (coniferous forest area). An obvious phenomenon of P limitation existed in the soil of the study area. There was a significantly positive correlation between soil C∶N and litterfall C∶N at different altitudes (r=0.40, P<0.05), while soil C∶P and N∶P were significantly positively correlated with soil moisture content (C∶P∶r=0.68, P<0.05). N∶P∶r=0.71, P<0.05), and were significantly negatively correlated with soil temperature (C∶P∶r=–0.35, P<0.05; N∶P∶r=–0.38, P<0.05) and pH (C∶P∶r=–0.60, P<0.05; N∶P∶r=–0.55, P<0.05). The results show that the variation of soil C∶N is mainly regulated by vegetation, factors, while those of C∶P and N∶P is mainly affected by soil physical and chemical factors.