Key influencing factors and spatiotemporal patterns of annual net ecosystem CO₂ exchange in China

Figuring out the influencing factors and spatiotemporal evolution of China's net ecosystem CO₂ exchange (NEE) is crucial for supporting the national dual carbon strategy goals. This study integrated 338 NEE observation records from 81 flux stations across China with multi-source remote sensing data to elucidate the spatiotemporal evolution of China's NEE since 2000. Results indicated that mean annual temperature (MAT), vapor pressure deficit (VPD), and bulk density (BD) were the primary factors influencing NEE variation in China. The dominant factor (MAT) exhibited a gradual stimulatory effect on NEE, with a turning point at 6.39 °C. From 2000 to 2023, China's annual NEE averaged -1.31 ± 0.19 Pg C yr^-1, exhibiting a sustained carbon sinks trend. During this period, the Three-North Shelterbelt Engineering Region (TNSER) contributed approximately 30% of China's terrestrial carbon sinks, demonstrating the positive impact of ecological engineering initiatives. Since 2003, the gap between China's terrestrial carbon sinks and anthropogenic CO₂ emissions has shown an expanding trend. The research findings provide scientific reference for national ecosystem carbon management needs and policy formulation from a carbon budget perspective.