Long-term manuring increases microbial carbon use efficiency and mitigates priming effect via alleviated soil acidification and resource limitation

No fertilized soils (unfertilized and fallow treatments) and soils subjected to 28-year fertilization regimes, including mineral fertilization (PK and NPK) and manure amendments (NPKM and M), were incubated with or without 13C - glucose. Results showed that compared to mineral fertilization (0.64 − 0.69), the manure amendments significantly increased microbial C use efficiency (CUE) (0.76 − 0.79), mainly due to higher soil pH, lower resource stoichiometric ratios of dissolved organic C (DOC): mineral N, DOC: available P and mineral N: available P, and lower specific activities (per microbial biomass C unit) of β-1,4-glucosidase, N-acetyl-glucosaminidase and acid phosphatase. Glucose addition increased SOC mineralization, inducing positive priming effect (PE) with lower values in the manure amendments (0.11 − 0.12 mg C g−1 SOC) relative to mineral fertilization (0.25 − 0.55 mg C g−1 SOC). The PE was negatively correlated with soil pH and positively associated with resource stoichiometric ratios of DOC: mineral N, DOC: available P and mineral N: available P, mainly due to microbes mineralizing SOM to release nutrients, as indicated by the positive relationships between PE and the specific activities of N-acetyl-glucosaminidase and acid phosphatase. Concluding, relative to mineral fertilization, long-term manure amendment could increase CUE and decrease PE via alleviated soil acidification and resource limitation, thus facilitating soil C sequestration.