Nitrogen Addition Promotes Soil Carbon Sequestration and Alters Carbon Pool Stability by Affecting Particulate Organic Carbon in a Karst Plantation

Increased global atmospheric nitrogen deposition can affect the accumulation and stability of forest soil organic carbon; however, the pathways and underlying mechanisms are largely unclear. In this study, we sampled soils from a karst plantation with four different nitrogen addition levels (0, 150, 300, and 600 kg N ha−2 yr−1), and we measured the soil organic carbon and chemical properties. We separated the soil organic carbon fractions and calculated the carbon pool lability on the basis of chemical and physical grouping. The results revealed that nitrogen addition significantly increased soil organic carbon and carbon pool lability on the basis of physical grouping, but it significantly decreased carbon pool lability based on chemical grouping. Particulate organic carbon was significantly correlated with the soil organic carbon and carbon pool lability, so it explained a high degree of the variance. In addition, nitrate nitrogen and easily oxidized carbon had significant impacts on soil organic carbon and carbon pool lability, respectively, on the basis of chemical grouping. Therefore, nitrogen addition promotes the soil carbon sequestration capacity and alters carbon pool stability by affecting particulate organic carbon. These findings deepen our understanding of the mechanism of forest soil carbon sequestration and stability in the context of future nitrogen deposition.