Straw return combined with water-saving irrigation improves soil quality and rice yield by regulating microbial community structure in paddy fields

While water-saving irrigation represents a promising water management practice for sustainable rice production, its impact on soil health in rice paddies remains controversial. Straw return offers a valuable natural solution for maintaining soil health and increasing rice yields in water-saving irrigated rice fields. However, it is unclear how returning straw under water-saving irrigation affects the physicochemical characteristics of the soil, rice yield, and soil microbial community, as well as the linkages and underlying mechanisms. To address these knowledge gaps, a 4-year experiment was conducted with four treatments: controlled irrigation (C); flooded irrigation (F); controlled irrigation with straw return (CS); and flooded irrigation with straw return (FS). High-throughput sequencing was used to explore the mechanisms by which soil microbial communities respond to irrigation and straw return, and to investigate the impact of microbial community activity on soil nutrient dynamics. The results showed that compared to flooded irrigation, controlled irrigation significantly reduced the α-diversity of soil fungi, decreased the relative abundance of bacterial communities (Proteobacteria and Actinobacteria), and increased bacterial chemotaxis. While combining straw return with water-saving irrigation does not lead to the adverse effects observed under water-saving irrigation alone. Straw return under different irrigation regimes significantly increased soil total nitrogen (TN) and soil organic carbon (SOC) content, with the greatest increase in the CS treatment. CS treatment enhanced soil microbial metabolic pathways related to the carbon and nitrogen cycle, leading to the highest soil nutrient levels and rice yield. Compared to other treatments, CS increased TN by 2.72 % to 9.88 %, SOC by 1.28 % to 9.31 %, and rice yield by 7.47 % to 36.94 %. Therefore, controlled irrigation combined with straw return represents a water-saving and yield-enhancing rice cultivation practice beneficial for long-term soil health. This study advances our understanding of soil microbial community activity and microbial-mediated changes in soil nutrient cycling under different water‑carbon regulation in rice paddies, providing valuable theoretical insights for maintaining soil health and sustainable cultivation in water-saving irrigated rice fields.