Gypsum application increases microbial activity and organic carbon mineralization in saline paddy soils

Abstract

Saline–alkaline soils, representing approximately 10 % of global soil resources, are characterized by high salinity and pH levels, low microbial activity, and inefficient soil organic carbon (SOC) accumulation. Gypsum application is a common practice for ameliorating saline soils, as it reduces exchangeable sodium and improves soil physicochemical properties. However, the impact of gypsum on soil microbial activity and organic carbon turnover remains insufficiently understood. Therefore, we conducted incubation experiments to investigate the effects of gypsum application on microbial community composition and OC mineralization in soils with varying salinity levels (154, 268, 646, and 865 μS cm⁻¹). Gypsum application significantly increased the mineralization of both glucose (exogenous organic carbon (EOC)) and SOC compared to the control (no gypsum), particularly in high-salinity soils, with increases of 282 % and 249 %, respectively. This enhancement was attributed to a 50 % reduced exchangeable sodium, which alleviated microbial salt stress and shifted microbial life strategies. Gypsum application also increased microbial abundance and decreased microbial diversity, favoring taxa growth that adapted to the reduced exchangeable sodium condition. Microbial network analysis revealed a 17.19 % increase in network edges and a 63-edge increase in high-salinity soils following gypsum application. Structural equation modeling indicated that improvements in environmental factors (e.g., soil ionic composition, +0.10) and microbial activity (+0.51) both contributed to the enhanced EOC mineralization after gypsum application. Overall, our findings suggest that gypsum application ameliorates high-salinity soils by boosting microbial activity and accelerating carbon utilization and mineralization, which holds significant implications for promoting EOC metabolism and SOC accumulation in saline soils.