Vertical distribution and impact factors of soil organic carbon in an alpine-cold zone of Northwest Sichuan

This paper studied organic carbon content, water content, pH value, available nitrogen content and available phosphorus content in different soil depths, and explored the correlations between organic carbon content and water content, pH value, available nitrogen content, or available phosphorus content of three typical soils (subalpine meadow soil, turfy meadow soil and alluvial soil) in Hongyuan County, Northwest Sichuan. Organic carbon content, water content, available nitrogen content, and available phosphorus content all had a downward trend with soil depth increasing both in subalpine meadow soil and in alluvial soil. With an increase in soil depth, the pH value increased in subalpine meadow soil. However, in alluvial soil, pH value decreased from 0-20cm to 20-40cm soil depth, had no significant variations among 20-40cm, 40-60cm, and 60-80cm soil depth, and increased from 60-80cm to 80-100cm soil depth. With soil depth increasing, organic carbon content and water content of turfy meadow soil both declined firstly, afterward increased, and reached the lowest content in the 20-40cm soil depth. With soil depth increasing, the pH value of turfy meadow soil rose firstly, afterward decreased and had the highest concentration in the 60-80cm soil depth. With soil depth increasing in turfy meadow soil, available nitrogen content and available phosphorus content changed and the changes had no obvious law. Organic carbon content, water content, available nitrogen content, and available phosphorus content were all the highest in turfy meadow soil, followed by in alluvial soil and then in subalpine meadow soil. Organic carbon content was significantly correlated with water content, pH value, available nitrogen content, or available phosphorus content in soils (P≤0.05), and the correlation coefficients were 0.984, -0.874, 0.699 and 0.717, respectively.