Net Carbon Uptake During the Wet Seasons Dominates Ecosystem Production in the Northernmost Mangroves in Southern China

Abstract Restored mangroves are increasingly recognized as vital nature‐based solutions for atmospheric CO 2 sequestration. We hypothesize that the seasonal dynamics of carbon fluxes and coupled regulatory mechanisms may be the key in understanding their sequestration strength, especially in the northernmost mangroves experiencing pronounced seasonality. In this study, we measured net ecosystem CO 2 exchange from 2017 through 2023 using the eddy covariance technique in the northernmost restored mangrove ecosystem in southern China. These mangroves acted as carbon sinks, with an annual net ecosystem production (NEP) of 530 g C m −2 . Throughout the study period, NEP was greater during the wet seasons than the dry seasons, primarily driven by elevated photosynthetically active radiation (PAR). Machine learning identified PAR as the most influential environmental driver of seasonal NEP differences, with its positive effect being significantly stronger in wet seasons compared to dry seasons ( p < 0.01). Air temperature (TA), soil temperature (TS), and soil water content (SWC) were also key drivers of NEP. When TA and TS exceeded thresholds of 27.81°C and 27.06°C, respectively, NEP was negatively affected, although such conditions occurred in 21% of whole observation period. High SWC had a more pronounced inhibitory effect on NEP during dry seasons, potentially because of reduced soil salinity impairing photosynthetic efficiency. As mangroves evolved, NEP's sensitivity to PAR and TA increased, while its sensitivity to TS and SWC was reduced. This study enhances our understanding of seasonal carbon fluxes and their interactions with environmental drivers in the northernmost restored mangrove ecosystem.