Synergistic mechanism of Bio-based sulfonate liquid in regulating organic carbon degradation and sequestration in calcareous soils

Calcareous soils in arid regions are characterized by high alkalinity and calcium content, which constrain the accumulation and stability of soil organic carbon (SOC). This study examined the effects of continuous application of Bio-based sulfonate liquid on SOC fractions, nutrient stoichiometry, microbial community structure, and carbon metabolic functions in calcareous cotton fields, using field experiments combined with multi-omics approaches. The co-application of Bio-based sulfonate liquid and chemical fertilizers significantly enhanced cotton yield by 13.53%-20.56%, while increasing soluble organic carbon and easily oxidizable carbon by 24.30% and 19.54%, respectively. Improvements in soil aggregate stability (MWD and GWD) facilitated the physical protection of SOC. Functional groups present in the Bio-based sulfonate liquid (e.g., C=C, C-O, -COOH) enhanced soil cohesion and promoted the activities of key carbon-degrading enzymes, including cellulase, sucrase, and β-glucosidase, thereby accelerating the turnover of recalcitrant organic matter. Positive correlations were observed among soluble Ca, N, P, available nutrients, and labile SOC fractions. Multi-omics analysis revealed a significant enrichment of carbon-metabolizing microbial taxa, such as Acidobacteria, Proteobacteria, and Gemmatimonadota. Additionally, genes associated with carbon cycling (e.g., lipase, cellulose synthase A3, β-glucosidase, acid phosphatase, 6-phosphogluconate dehydratase ) were markedly upregulated. Metabolic pathways related to starch, sucrose, and galactose were activated, enhancing carbon availability for microbial communities. These findings provide mechanistic insights into the chemical and biological processes regulating SOC transformation in calcareous soils, and offer a scientific basis for sustainable straw resource utilization and carbon sequestration strategies in arid agricultural systems.