Abstract: The terrestrial carbon cycle is an important component for researches on climate change and global carbon cycle. Net ecosystem productivity (NEP) is an essential indicator to quantitatively describe the carbon source/sink capacity of vegetated ecosystems. The grassland ecosystem is an important part of the global terrestrial ecosystem, and the Hulun Lake Basin is a multi-ecosystem area dominated by grassland ecosystem and mixed with farmland, forest and wetland ecosystems. The spatiotemporal variations and drivers of its carbon source/sink are of great significance in the study of ecological environmental protection and restoration as well as the local climate change in this region. Based on Landsat 8 OLI high-resolution satellite remote sensing images, ERA5 climate reanalysis data and land cover data, the spatiotemporal patterns of carbon sinks of different vegetation types in the Hulun Lake basin from 2013 to 2020 and their differences in response to climate factors were estimated using a light use efficiency model and a soil respiration model. The results show that since 2013, the Hulun Lake Basin has been functioning as a carbon sink, while the carbon sequestration capacity decreased, with 58.29% of the regional vegetation NEP showing a decreasing trend and 36.77% of the regional vegetation NEP showing a weak increasing trend. The regional monthly average NEP showed inter-annual variation characteristics of firstly decreasing and then increasing, with a variation range of 8.41-16.44 g·m^-2·mo^-1, In the watershed, the grassland ecosystem had the highest total carbon sink, about 37 Tg·mo^-1, and the farmland NEP was mostly affected by temperature, and the forest ecosystem was influenced by the combination of temperature, precipitation, and radiation. The grassland ecosystem is concurrently affected by temperature and precipitation, while the wetland NEP is not significantly correlated with climate factors.

Key words: net ecosystem productivity, carbon source/sink, Hulun Lake Basin, GEE, ERA5