###### Abstract  
Terrestrial ecosystem carbon uptake is essential to achieving a regional carbon neutrality strategy, particularly in subtropical humid areas with dense vegetation. Due to the complex spatial and temporal heterogeneity of the carbon uptake of ecosystems, it is difficult to quantify the influence and contribution of different factors. With the aid of multisource remote sensing data, the spatiotemporal characteristics of carbon uptake and the impact of vegetation change were explored in the Dongting Lake Basin from 2001 to 2020. Based on the Conversion of Land Use and its Effects at Small regional extent (CLUE-S) model, we simulated the land use of the basin under different development scenarios in 2030. Our results showed that the basin has demonstrated a significant greening trend in the last 20 years, with a multiyear average NDVI (normalized difference vegetation index) of 0.60 and an increasing trend (\(y=0.0048x-9.069\), \(R^{2}=0.89\), \(p<0.01\)). In this context, the multiyear mean of net ecosystem productivity (NEP) was 314.95 g C\(\cdot\)m\({}^{-2}\)-a\({}^{-1}\) and also showed a significant increasing trend (\(y=1.8915x+295.09\), \(R^{2}=0.23\), \(p<0.05\)). Moreover, though the future carbon uptake might decrease because of the enhanced anthropogenic activities, the ecological conservation scenario might mitigate the reduction by 0.05 \(\times\) 10\({}^{7}\) t. In conclusion, the greening trend enhanced the ecosystem carbon uptake in the Dongting lake basin. Considering the representativeness of the Dongting Lake Basin, the results of our study would provide useful clues for understanding the trend and pattern of terrestrial carbon uptake and for guiding the carbon neutrality strategy in the subtropical humid area. terrestrial carbon uptake; vegetation change; climate change; CLUE-S model; Dongting Lake Basin +
Footnote †: journal: Physics Letters B  
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Footnote 1: institutetext: School of Geosciences and Info-Physics, Central South University, Changsha 410083, China  
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terrestrial ecosystem carbon sequestration has also become an important prerequisite for regional carbon trading and management [7]. The main methods for monitoring carbon uptake in ecosystems are the sample plot inventory method, model simulation method, and quantitative remote sensing method [5]. Among them, the sample plot inventory method is used to investigate the carbon stocks of vegetation, litterfall, soil, and other carbon pools in ecosystems by setting up typical sample plots and to obtain the changes in carbon stocks over a certain period of time based on long-term continuous measurements, which is more accurate but difficult to apply to regional large-scale uptake monitoring and analysis [8]. The model simulation method uses photosynthesis and respiration in vegetation growth to simulate its growth cycle and its key processes with solid physical mechanisms, but the assumptions and structures of different models vary greatly. Additionally, the complexity of input parameters would also generate the unavoidable uncertainty [8]. The quantitative remote sensing method provides an efficient way to track and analyze regional large-scale ecosystem carbon uptake based on remote sensing techniques to obtain various vegetation parameters. This method is then combined with ground survey data and empirical models to estimate carbon storage [9]. Carbon uptake monitoring of terrestrial ecosystems based on satellite remote sensing mainly utilizes the accurate inversion of ecological indicators such as gross primary productivity (GPP), net primary productivity (NPP), and net ecosystem productivity (NEP) [10]. NEP shows the net CO\({}_{2}\) exchange between ecosystems and the atmosphere, showing how much carbon is stored in a certain area. When NEP > 0, the ecosystem behaves as a carbon sink, meaning that it sequesters more carbon from the atmosphere than it releases to the atmosphere. In addition, when NEP < 0, it behaves as a carbon source, meaning that it releases more carbon to the atmosphere [11].