Irrigation regimes regulate carbon and nitrogen cycling to reduce greenhouse gas emissions intensity while maintaining yield in dry direct-seeded rice

Understanding the effects of irrigation regimes on the carbon (C) and nitrogen (N) cycles in paddy soils and their association with yield and greenhouse gas emissions is crucial for improving rice soil fertility and promoting sustainable ecosystem development. However, it has not been fully understood. This study was based on a long-term field experiment to compare dry direct seeding rice (DDSR) with traditional flooding irrigation rice (TFIR). The results showed that compared with TFIR, DDSR significantly changed the soil nutrient status, increased NO 3 - -N and available potassium, and decreased NH 4 + -N and available phosphorus. Functional analysis showed that irrigation regimes significantly affected the carbon and nitrogen cycling pathways of soil microorganisms. Compared with TFIR, DDSR enhanced fermentation and methane metabolism, while reducing carbon fixation and decomposition. In the nitrogen cycle, DDSR promoted dissimilatory and assimilatory nitrate reduction (DNRA and ANRA), but inhibited nitrification and denitrification. These changes in soil processes lead to significant differences in greenhouse gas emissions. Compared with TFIR, DDSR reduced the cumulative CH 4 emissions by 70.60%-72.98%, but increased the emissions of CO 2 and N 2 O. Overall, DDSR significantly reduced global warming potential (GWP) by 47.75% −52.95% and greenhouse gas intensity (GHGI) by 45.79%-51.47%. The magnitude of these reductions varied between years, likely due to interannual variations in precipitation, temperature, and soil moisture dynamics, which influence microbial carbon and nitrogen transformation processes. However, the rice yield under DDSR treatment was slightly lower than that under TFIR treatment, but the difference was not significant. Further studies showed that soil pH, SOC and nutrient availability were associated with variations in carbon and nitrogen cycling pathways, and jointly regulated yield, GWP and GHGI. In summary, water-saving irrigation in DDSR effectively reduced global warming potential and greenhouse gas intensity under the premise of stable production by changing soil physical and chemical properties and regulating soil carbon and nitrogen cycle processes. These findings provide a scientific basis for optimizing irrigation regimes for sustainable rice production.