Extracellular polymeric substances regulate depth-and-season-dependent soil organic carbon stabilization under...

This study explores the dynamics of soil organic carbon (SOC) in karst ecosystems under prescribed fire and seasonal variations, emphasizing the role of deeper soil horizons often overlooked in previous research. We investigated the influence of fire and seasonality on extracellular polymeric substances (EPS) production at two soil depths (0-10 cm and 20-30 cm) in burned and unburned soils. EPS-protein content ranged from 3.09 to 7.52 mg kg^-1 in burned soils and 3.09 to 5.34 mg kg^-1 in unburned soils, with higher concentrations at 20-30 cm in burned soils during the dry season. EPS-polysaccharide content was highest in unburned soils (9.92 mg kg^-1) at 0-10 cm during the wet season. Amino sugar levels varied significantly, with Glucosamine concentrations reaching 99.96 mg kg^-1 in burned soils at 20-30 cm in the dry season. Microbial biomass carbon (MBC) and nitrogen (MBN) displayed significant seasonal and depth-dependent variations, with higher MBC:SOC ratios in burned soils during the dry season at 0-10 cm. Enzyme activities, including acid phosphatase, β-glucosidase, and N-acetylglucosaminidase, were higher in unburned soils, indicating more active nutrient cycling. Structural equation modeling and Random Forest analysis identified soil nutrients, EPS-protein, and microbial biomass as key drivers of the EPS-C:SOC ratio. These findings highlight the importance of deeper soils in SOC stabilization and provide new insights into the impacts of fire and seasonality on microbial processes, enhancing our understanding of carbon sequestration in karst ecosystems.