The Dominant Factor Affecting Soil Organic Carbon in Subtropical Phyllostachys edulis Forests Is Climatic Factors Rather Than Soil Physicochemical Properties

Phyllostachys edulis, also known as moso bamboo, is widely distributed in China, has strong carbon sequestration potential, and contributes significantly to carbon sinks at the regional scale. However, the distribution and influencing factors of soil organic carbon (SOC) are unclear in bamboo forests at the regional scale. We selected six sites in Phyllostachys edulis forests in the northern subtropics, middle subtropics, and southern subtropics of China to determine the SOC contents and estimate its stocks. The relationships between the SOC and geographic position, climate, vegetation, and the soil’s physical and chemical characteristics were analyzed via Pearson correlation coefficients. Structural equation modeling (SEM) was established to reveal the direct and indirect effects of all factors on the SOC. The SOC content significantly decreased with an increase in soil depth in the subtropics. The Pearson correlation analysis and structural equation modeling results indicated that the climate was closely related to and had the most significant effect on the SOC in moso bamboo forests. The maximum effect values of the annual mean temperature (MAT) and annual mean precipitation (MAP) on SOC were −0.975 and 0.510, respectively. Elevation and latitude were strongly correlated with Phyllostachys edulis forests and 0–10 cm SOC content and significantly contributed to the SOC with effect values of 0.488 and 0.240, respectively. The soil’s physical properties and forest biomass had significant negative effects on the SOC. Both NH4+-N and available phosphorus (SAP) were significantly and positively correlated with the SOC at different soil depths in moso bamboo forests to different degrees, but he soil’s chemical properties, in general, had no significant direct effect on the SOC.