Deciphering Differential Soil Carbon Mineralization Under Organic Amendments: Linking Enzyme Stoichiometry, Microbial Communities, and Functional Genes in Tibetan Agroecosystems

ABSTRACT Organic amendments (OAs) are recognized as a promising strategy for enhancing soil organic carbon (SOC) stocks in agroecosystems. However, the effects of different OAs combined with chemical fertilizers (CF) on carbon (C) mineralization and how microorganisms mediate this process remain poorly understood. Here, to examine the effects of different fertilization management practices on SOC mineralization, an 85‐day incubation experiment was conducted using farmland soil from the Lhasa Valley, Tibetan Plateau. Six treatments were established: no‐fertilizer control (CK), pure urea treatment (U), and four OAs replacing 40% of urea, namely compost (CP), yak dung (YD), Qingke straw (QS), and Tibetan sheep dung (SD). We further explored relationships between SOC mineralization and soil physicochemical properties, enzyme stoichiometry, C‐cycling functional genes, and microbial community composition. Results indicated that cumulative CO 2 emissions were significantly higher under all fertilization treatments than in the CK. Among the fertilization treatments, the highest cumulative CO 2 emissions were observed in the QS treatment at 763.77 mg/kg, while the lowest were in the CP and U treatments at 192.36 and 166.46 mg/kg, respectively. Moreover, significant positive correlations were observed between CO 2 emissions and soil labile organic C (LOC), extracted organic C (EOC), dissolved organic C (DOC), and microbial biomass C (MBC). Fertilization alleviated soil microbial C limitation but exacerbated phosphorus (P) limitation while increasing C‐cycling gene abundance, particularly for cbhI in the QS treatment. OAs significantly altered microbial community structure, promoting high C–preferring taxa such as Proteobacteria. Bacterial networks were more complex, stable, and sensitive to nutrient availability than fungal networks in driving SOC mineralization. Key predictors of cumulative CO 2 emissions included C source availability (e.g., MBC, DOC, and LOC), C‐cycling functional genes (e.g., cbhI ), total P, and alkaline phosphatase activities. Under equivalent N input, CP most effectively mitigated soil CO 2 emissions and maintained relative soil C stability, whereas QS showed greater potential to promote the turnover of labile C. Accordingly, we recommend prioritizing compost application in farmlands of the Lhasa Valley, supplementing OAs with P to alleviate nutrient limitations, and avoiding excessive application of untreated straw to minimize short‐term carbon loss. These locally tailored, microbe‐ and soil‐aligned strategies support sustainable SOC enhancement and high‐altitude agricultural.