Exceptional carbon sink potential of Shenzhen mangroves and a machine-learning framework for addressing sparse global observations

Background: Coastal mangrove wetlands have great carbon sequestration potential, but assessments lack precision due to limited CO₂ flux monitoring stations. This study aims to clarify the variation patterns and mechanisms of carbon sinks in typical mangrove ecosystems and propose a viable framework to address sparse CO₂ flux station coverage. Methods: This study systematically investigated the carbon sequestration potential, temporal dynamics, and driving mechanisms of mangroves in the Futian Mangrove Nature Reserve, Shenzhen, via eddy covariance (EC) observations and machine learning-based modeling, while conducting multi-scale comparative analyses with regional and global mangrove ecosystems. Results: Results revealed that the Shenzhen mangrove ecosystem maintained a robust net carbon sink capacity during the study period. Monthly net ecosystem production (NEP) was lower in August and higher in December, a pattern primarily driven by attenuated nighttime respiratory activity in the dry season. Further comparative analyses highlighted the Shenzhen Futian mangroves as a high-efficiency carbon sink at both regional and global scales, with the annual NEP of 1265.5 g C m⁻² a⁻¹, which is higher most of the investigated sites in this study. This high NEP in Shenzhen likely arises from the synergistic interplay of a favorable subtropical marine monsoon climate, the resilience of native species, and advanced conservation management practices. Furthermore, we developed a data-driven RF regression-based NEP prediction model integrating multi-source environmental variables, which achieved good predictive performance for the Shenzhen observations and showed preliminary transferability to two congeneric Kandelia-dominated mangrove sites. Conclusions: This study provides a novel framework to address the critical gap of sparse EC station coverage in global mangrove ecosystems. These findings may help refine mangrove blue-carbon accounting and provide methodological support for future Monitoring, Reporting, and Verification (MRV) systems and coastal wetland management.