Optimizing multi-system coupling to mitigate carbon emissions in agrifood systems at county level in China.

The growing demand for food has led to overuse of land, exacerbating the environmental sustainability of agrifood systems. Insufficient coordination and coupling within agrifood systems (soil-crop-animal-food consumption) reduce material cycle efficiency and limit the system's carbon reduction potential. Given the lack of global research on the impact of system coupling on carbon reduction, the value of regional practice cases is particularly evident. To address this issue, we propose a systematic, integrated multiple-methods framework-agrifood systems carbon and nitrogen (AFS-CN)-that considers the feedback mechanisms between system coupling, carbon balance, and nitrogen management. This framework is applied to a typical county in Zhejiang Province, China, which is characterized by a high level of economic development and diverse agricultural production patterns. The results indicate that the AFS-CN framework can link subsystem coupling coordination with soil carbon sequestration and crop-animal-food consumption carbon emissions. The crop subsystem is the primary emission source, accounting for 72 %-83 % of total carbon emissions, followed by the food consumption subsystem, while the soil subsystem plays a minor role in carbon sequestration. As agrifood systems coupled coordination degree (CCD) increases, carbon emissions initially decrease rapidly before gradually flattening out. When the CCD exceeds 0.6, the trend of carbon emissions reduction begins to slow down. The soil subsystem indirectly exerts a net positive influence on the food consumption subsystem through the crop subsystem. This study provides new perspectives and methods for understanding the coupling coordination mechanisms of the agrifood systems and formulating carbon emissions reduction strategies.