Straw plus straw interlayer alter soil organic carbon and bacterial community in a saline-alkali soil from the Yellow River Delta

Salt stress and nutrient deficiency severely restrict soil carbon storage and microbial diversity in the Yellow River Delta. Soil amendments has been widely recognized as an effective approach to improving saline-alkali soil fertility. However, the effects and interactions of straw return plus desulfurized gypsum or straw interlayer on soil carbon content and bacterial communities remain unclear. We conducted field experiments with five treatments: (1) no addition (CK), (2) straw return alone (S), (3) straw return plus desulfurized gypsum (DG_S), (4) straw return plus straw interlayer (SL_S), and (5) straw return plus desulfurized gypsum plus straw interlayer (DG_SL_S). The results indicated that compared with straw return alone, DG_S, SL_S, and DG_SL_S further improved soil nutrient availability, with DG_S and SL_S increasing SOC by 25.1 % and 33.26 %, respectively. Conversely, DG_S, SL_S, and DG_SL_S significantly reduced DOC content, whereas DG_S and DG_SL_S reduced MBC by 8 % and 10.81 %, respectively. All amendment treatments significantly enhanced soil enzyme activities. Alpha and beta diversity analysis indicated that the amendment treatments significantly enhanced bacterial richness, diversity, and altered community structure. Compared with the straw return alone, straw return plus straw interlayer showed significantly higher relative abundances of Gemmatimonadota , Chloroflexi , Aquicella, and Salinimicrobium , and lower Actinobacteria . DOC, MBC, β-1, 4-glucosidase, and cellobiohydrolase were core drivers of bacterial community changes. Bacterial co-occurrence network analysis demonstrated that DG_S and SL_S treatments enhanced bacterial community stability, complexity, and connectivity compared with straw return alone, thereby promoting organic carbon cycling and sequestration. Functional predictions indicated all amendments optimized soil carbon sequestration and nutrient conversion by enhancing carbohydrate metabolism, lipid metabolism, and nitrogen sulfur cycling, and reducing the TCA cycle. In conclusion, our findings demonstrate that straw combined with desulfurized gypsum or straw interlayers significantly enhances bacterial diversity and soil fertility, emerging as effective strategies for sustainable agriculture in the Yellow River Delta.