Long-Term Understory Rotary Tillage Incorporation Enhances Plain Plantation Growth by Synergistic Regulation of Soil and Microbial Properties

To investigate the effects of long-term continuous rotary tillage incorporation (RT) on Fraxinus chinensis Roxb. plantations, this study compared 7- and 15-year-old stands subjected to RT since afforestation with their non-tilled counterparts (CK). Results demonstrated that RT significantly enhanced tree growth by synergistically improving soil nutrient availability, physical properties, and microbial community structure and function: (1) Compared with CK, RT increased diameter at breast height (DBH) by 28.89% in 7-year-old stands and 22.58% in 15-year-old stands, and tree height by 19.51% in 7-year-old stands and 25.00% in 15-year-old stands; (2) RT increased contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP), rearranged the distribution patterns of soil particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and reduced soil bulk density (BD) and soil water content (SWC); (3) RT regulated microbial diversity, co-occurrence networks, and carbohydrate-degrading gene abundances, with more prominent effects in 15-year-old stands. This tillage practice is feasible and effective, and thus is recommended for application in F. chinensis plantation management, providing a scientific basis for refined and sustainable plantation management.