Effects of co-application chemical and organic fertilizers on microbial residues and their contribution to soil organic carbon accumulation.

Background: Fertilization strategies in agricultural ecosystems significantly influence soil organic carbon (SOC) dynamics, and integrated chemical and organic fertilization may enhance short-term SOC accumulation. However, the mechanisms, particularly the contribution of microbial residues to SOC dynamics during the crop growth period, remain unclear. Methods: In this study, we evaluated four fertilization treatments in tobacco-planting field under a randomized block design with three blocks: (1) no fertilizer (CK), (2) chemical fertilizer (CF), (3) chemical fertilizer with corn straw amendment (CFS), and (4) chemical fertilizer with manure amendment (CFM). Soil samples (0-20 cm) were collected at six stages of the tobacco-growing period, and were analyzed for SOC, soil physicochemical properties, and amino sugar biomarkers (MurA, GalN, and GluN) to calculate microbial residue-C fractions. Results: Fertilization significantly affected soil nutrient status, amino sugar pools, microbial residue-C fractions, and SOC over time compared with CK and CF, the two organic-amended treatments were associated with higher SOC concentrations, and CFM showed the strongest short-term SOC response (peaked at 10.30 ± 0.22 g kg Conclusion: Integrated chemical-organic fertilization, particularly CFM, favored short-term SOC accumulation in tobacco-planting soil. Amino sugar-derived microbial residues were also enhanced under organic-amended fertilization, and bacterial residues were more closely associated with SOC than fungal residues during the observed period. The merged piecewise linear mixed-effects SEM indicated that short-term SOC dynamics were driven mainly by fertilization regime and temporal variation, providing region-specific evidence for optimizing fertilization strategies in tobacco-planting red soils of Yunnan.