Grass mulching has been proven to effectively enhance soil organic carbon accumulation and improve soil fertility in orchard systems. However， the mechanisms regulating the dynamics of labile organic carbon and humified carbon fractions remain unclear. From 2021 to 2023， a field experiment was conducted in an apple orchard with four grass mulching treatments established in both interrow and tree disk areas： perennial ryegrass （Lolium perenne L.）， sweet clover （Melilotus officinalis L.）， perennial ryegrass + alfalfa （Medicago sativa L.）， with traditional clean tillage as the control （CT）. We analyzed soil labile organic carbon fractions， humic carbon fractions， carbon-cycling enzyme activities， and the carbon pool management index. The results showed that sweet clover significantly increased soil organic carbon content by 14.38% and elevated the carbon pool management index by 89.55% in the interrow area compared to CT in 2022 （P<0.05）. In 2023， sweet clover further reduced soil pH in the interrow areas and the bulk density of the tree disk areas. Meanwhile， the perennial ryegrass + alfalfa mixture treatment increased soil organic carbon by 19.19% in the tree disk area， with concurrent rises in dissolved organic carbon and microbial biomass carbon （P<0.05）. Mantel tests and partial least squares path modeling revealed distinct responses of the interrow and tree disk areas to grass mulching. Increased labile organic carbon fractions primarily characterized the interrow areas， while the tree disk areas showed a strong positive response in humified carbon accumulation. In conclusion， sweet clover performed the best in interrow areas， while the perennial ryegrass + alfalfa mixture was the most effective in tree disk zones. Grass mulching in apple orchards can positively regulate the soil carbon pool through improvements in soil physical structure， activate carbon-cycling enzymes， and increase soil carbon fractions.

Soil organic carbon  /  Labile organic carbon  /  Humic carbon  /  Soil enzyme activity  /  Carbon pool management index  /  Grass mulching in orchards