## 5 Conclusions  
Based on the data of the MODIS net primary productivity product MOD17A3H and land cover product MCD12Q1, combined with monthly mean temperature and precipitation data, this paper calculated the _NEP_ values in the Yangtze River Delta region from 2000 to 2019, obtained its spatial distribution information and change characteristics, and  
Figure 10: Interannual variation of _NEP_, annual average temperature, and annual rainfall in the Yangtze River Delta.  
analyzed its correlation with the annual mean temperature and annual precipitation data of the Yangtze River Delta region. The main conclusions are as follows:  
1. From 2000 to 2019, the carbon sink area in the Yangtze River Delta was much larger than the carbon source area, the mean \(NEP\) of the vegetation ecosystem in the past 20 years was 253.2 g C\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), and the spatial distribution presented a trend that was higher in the south and lower in the north, higher in the east and lower in the west, and gradually increasing from northwest to southeast, and showed that the \(NEP\) of mountain areas is generally higher than that of river courses and urban surroundings. From 2000 to 2019, the \(NEP\) value of the vegetation ecosystem in the Yangtze River Delta region had small interannual fluctuations; however, the changes in various years were not large and presented a slightly increasing trend, and the interannual variation of the \(NEP\) was significantly correlated with the maximum \(NEP\) in this region;
2. The carbon sink capacities of different vegetation cover types and terrestrial vegetation ecosystems were different. The carbon sink capacity can be divided into three levels: the carbon sink capacity of woodland is better than that of grassland, and the carbon sink capacity of grassland is better than that of wetland and cultivated land;
3. From 2000 to 2019, the area of the Yangtze River Delta region had a change rate of \(NEP\) value greater than 0 and accounted for 69.0%; however, there were certain spatial differences. The proportions of provinces and municipalities with \(\theta_{slope}<0\) in this region are 14.50% (Zhejiang Province), 9.10% (Anhui Province), 6.65% (Jiangsu Province), and 0.79% (Shanghai); however, in terms of the changes of each province and municipality, Shanghai of China accounted for the largest proportion, followed by Zhejiang Province of China; the proportions of Jiangsu Province of China and Anhui Province of China were smaller;
4. The carbon sink of the terrestrial vegetation ecosystem in the Yangtze River Delta region is a complex process, and there is no significant correlation between its \(NEP\) and the annual mean temperature and annual precipitation factors, indicating that the capacity is not only related to the plants' own characteristics and external environment, but are also affected by human activities.  
Investigation, Methodology, Software, Validation, Formal analysis, Visualization, Writing--original draft, C.Z.; Funding acquisition, Project administration, Resources, H.L.; Investigation, Methodology, D.C.; Software, Cartography, J.F. and Z.L.; Remote sensing image processing, X.X. and Z.W.; Evaluation, J.L.; All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Anhui Science and Technology Major Program [grant number 202003a06020002], Anhui Province key research and development plan [grant number 2021003, 202104A07020002], Anhui Province Fifth Special Support Program, Anhui University Collaborative Innovation Project [grant number GXXT-2021-048], Anhui Provincial Natural Science Foundation [grant number 2008085 QD166].  
Not applicable.  
We would like to thank the forestry administration of ChuZhou City, Anhui Province.  
The authors declare no conflict of interest.