Abstract: Paddy field is a major source for global greenhouse gas emissions (GHGs). The implementation of coordinated water-nitrogen regulation has emerged as an effective approach to mitigate GHGs in paddy field. Taking Changgang irrigation area in Heilongjiang Province as the study area, we synthesized field experiment monitoring, mechanistic model simulations and optimization modeling to establish a multi-objective optimization regulation model. The model holistically incorporated yield enhancement, the efficient utilization of water and nitrogen resources, and emission reductions. With this model, we systematically evaluated the regulatory impacts of water-nitrogen optimization on GHGs, and ecological and agronomic benefits. The results showed that the optimized water-nitrogen regulation scheme prioritized irrigation water allocation during the tillering and jointing-booting stages, with nitrogen fertilizer application concentrated predominantly in the tillering phase. Under the optimized scheme, stable rice yields were sustained across the four hydrological zones of the Changgang irrigation area, while achieving water savings of 19.1%-22.2%, reducing fertilizer inputs by 13.2%-20.0%, enhancing water use efficiency by 0.8%-2.2%, increasing nitrogen partial productivity by 17.9%-27.9%, and decreasing Global Warming Potential by 5.96%-6.10%. These findings demonstrate that optimized water-nitrogen regulation strategies could enhance water and nitrogen use efficiencies, maintain rice productivity, and reduce GHGs. This study provides a scientific foundation for advancing sustainable development goals characterized of low emissions, high efficiency, and high yield in paddy ecosystems.

Key words: paddy ecosystem, greenhouse gas emission, water-nitrogen optimization management, emission reduction-high efficiency-high yield synergy