Effects of Forest Restoration on Soil Carbon, Nitrogen, Phosphorus, and Their Stoichiometry in Hunan, Southern China

Forest restoration affects nutrient cycling in terrestrial ecosystems. However, the dynamics of carbon (C), nitrogen (N), and phosphorous (P), and their stoichiometry (C:N:P ratio) in the soil during forest restoration are poorly understood in subtropical areas. In the current study, we collected soil samples at three depths (0-10, 10-20, and 20-30 cm) at three restoration stages (early, intermediate, and late) in subtropical forests. Soil organic carbon (SOC), total nitrogen (N), and total phosphorous (P) concentrations were determined. Forest restoration significantly affected soil nutrient concentrations and stock (p < 0.05). SOC concentrations increased from 12.6 to 18.6 g/kg and N concentrations increased from 1.2 to 1.6 g/kg, while P decreased from 0.3 to 0.2 g/kg. A similar pattern of change was found for the nutrient stock as restoration proceeded. C:P and N:P ratios increased to a greater extent than that of C:N ratios during forest restoration, implying that subtropical forests might be characterized by P limitation over time. The slopes and intercepts for the linear regression relationships between SOC, N, and P concentrations were significantly different across the forest restoration stages (p < 0.05). This indicated that forest restoration significantly affects the coupled relationships among C-N, C-P, and N-P in subtropical forest soil. Our results add to the current body of knowledge about soil nutrient characteristics and have useful implications for sustainable forest management in subtropical areas.