Effects of water-saving irrigation on greenhouse gas emissions: a meta-analysis of multi-factor mechanisms across Chinese coastal and inland regions

Under the escalating pressures of climate change and freshwater scarcity, understanding how irrigation management alters greenhouse gas dynamics in agricultural ecosystems has attracted increasing attention. This study conducted a comprehensive meta-analysis based on 76 field-derived publications across Chinese coastal and inland regions. We evaluated the impacts of water-saving regimes-including deficit, alternate, and intermittent irrigation-on field emissions of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2), with random forest (RF) modeling and path analysis employed to disentangle the underlying mechanisms. The results demonstrated that water-saving practices induced a distinct biogeochemical divergence in field agroecosystems, characterized by a significant comprehensive effect of “CH4 reduction, N2O promotion, and minor CO2 mitigation” (log response ratios, ln RR=-0.48, 0.28, and -0.09, respectively). Specifically, intermittent irrigation exerted the most pronounced impact, with both CH4 mitigation (ln RR=-0.51) and N2O promotion (ln RR = 0.52) reaching their peak intensities. Driven by spatial hydrothermal heterogeneity, the Southeast Coastal region exhibited the highest sensitivity in gas flux responses. Conversely, North China showed the lowest risk of N2O promotion (ln RR = 0.12) while maintaining robust mitigation capacity. RF modeling and meta-regression identified geographical region, soil pH, and soil organic matter (SOM) as the core predictors for the variances in CH4 (R2 = 55.2%), N2O (R2 = 59.4%), and CO2 (R2 = 48.1%) effects, respectively. Crucially, regression models pinpointed neutral-to-alkaline conditions (pH 7.0-7.2) as the critical threshold for N2O responses, beyond which alkaline soil conditions were associated with a transition from N2O promotion to mitigation. Path analysis further confirmed that irrigation modes exerted the strongest direct negative effect on CH4. Soil pH showed a highly significant direct inhibition on N2O, whereas precipitation introduced a notable indirect positive effect on N2O by driving soil acidification; meanwhile, SOM showed a dominant direct contribution to CO2 mitigation. In conclusion, the environmental feedback of water-saving irrigation is a product of deep coupling between technical interventions and natural backgrounds. Future mitigation policies must integrate a “smart-adaptation” framework tailored to regional precipitation, soil pH, and SOM matrices, thereby orchestrating a synergy between watershed-scale green agricultural development and carbon neutrality goals.