Soil extracellular enzymatic stoichiometry, the ratio of soil enzyme activities related to the acquisition of nutrients such as carbon (C), nitrogen (N), and phosphorus (P), which can reflect the demand for resources by microorganisms. However, how cover crop and chemical fertilizer shift microbial nutrient limitation as indicated by soil enzymatic stoichiometry in apple orchard remains unclear. Here, we determined microbial metabolic limitation by soil enzymatic stoichiometry, and to clarify how this affected soil microbial carbon use efficiency (CUE). The orchard experiment was conducted in two main plots comprising cover crop (GC) and no cover crop (C) with two subplots comprising no fertilization (CK) and N, P, and K fertilizer (NPK). The activity of C, N, and P acquisition enzymes (β-1,4-glucosidase, BG; leucine aminopeptidase, LAP; β-1,4-N-acetylglucosaminidase, NAG; and acid or alkaline phosphatase, PHOS), soil nutrient contents, plant nutrient contents, and microbial biomass were determined. Cover crop and fertilization significantly affected the soil properties, microbial biomass, and enzymatic stoichiometry in different stages and distances. The microbial biomass C (microC), N (microN) and P (microP) were significantly higher under cover crop than no cover crop in the germination and mature stage of apple trees, especially at the distance of 90 and 120 cm. Characteristics of enzymatic stoichiometry indicating strong C and P limitation in the microbial community during the plant growing stages, and were highest at the distance of 90 and 120 cm. AP and AN were the most important soil physicochemical factors that affected vector length and angle. The microbial C and P limitations were significantly correlated with microbial CUE (p < 0.001). Our results showed that how cover crop and fertilizer mediated microbial C and P metabolism during the growing stages of apple trees, which has implications for understanding the mechanism of soil C turnover under cover crop and fertilization in apple orchards
