Objective The aims were to clarify the response characteristics of comprehensive water-fertilizer improvement measures to basic properties of coastal saline soil and soil microbial community structure, in order to provide a scientific basis for the efficient utilization and development of saline soil resources in coastal areas.

Method the typical saline soil in Tianjin coastal area was taken as the research object, and three treatments of dry field (CK), dry modified paddy field (W) and dry modified paddy field combined with bio-organic fertilizer (BW) were designed. The effects of different treatments on salt reduction and alkali regulation of coastal saline soil, and the response characteristics of soil bacterial community to environmental changes were analyzed.

Result Compared with CK, the BW treatment significantly reduced soil EC and pH (by 4.1% and 5.8%, respectively), increased soil organic carbon and available phosphorus content (by 17.2% and 17.9%, respectively), and enhanced soil urease and alkaline phosphatase activities (by 25.8% and 126%, respectively). The BW treatment also significantly increased bacterial richness and promoted the enrichment of beneficial bacterial groups such as Acidobacteriota (relative abundance increased by 39%) and Gemmatimonadota. Functional prediction revealed that the BW treatment significantly enhanced the abundance of microbial taxa involved in sulfur and nitrogen cycling, such as Desulfosarcinaceae and Desulfocapsaceae.

Conclusion The combination of converting dryland to paddy field with bio-organic fertilizer application improved the coastal saline soil environment by reducing soil pH and EC, increasing nutrient contents such as organic carbon and available phosphorus, optimizing microbial communities associated with nitrogen and sulfur transformation, and enhancing ecological functions. This approach represents a viable strategy for microecological restoration of saline soils.