Long-Term Net Harvesting Is Associated with Elevated Soil Carbon Pool Management Index in Chinese Hickory Plantations

As the unique edible nut species in China, Chinese hickory (Carya cathayensis Sarg.) is vulnerable to anthropogenic disturbances that reduce vegetation residue inputs and soil organic matter accumulation. To investigate the effects of net-harvesting-associated understory management on the soil carbon pool management index (CPMI), soil samples were collected from C. cathayensis plantations subjected to net harvesting for 2, 3, 6, and 7 years, with traditional beating as the control. Long-term net harvesting significantly increased particulate and dissolved organic carbon, microbial biomass carbon, and labile organic carbon (p < 0.05). It also altered soil enzyme activities, microbial community composition, and microbial co-occurrence network complexity. Soil physical and chemical properties and carbon pools were key drivers of enzyme activities and microbial complexity. Partial least squares path modeling (PLS-PM) revealed that understory vegetation positively influenced the CPMI (total effect = 0.57), while soil biological processes also contributed to CPMI variation. Overall, net harvesting reduced anthropogenic disturbance, enhanced litter-derived carbon inputs, and promoted soil biological functions, thereby improving the CPMI. These findings provide insights into sustainable soil management and carbon sequestration in C. cathayensis plantations.