Carbon dioxide fluxes over grassland ecosystems in the Middle Tianshan region of China with eddy covariance method

Abstract Grassland ecosystems are an important component of global terrestrial ecosystems and play a critical role in the carbon cycle of ecosystems. It is important to study the Carbon dioxide (CO 2 ) process in the Middle Tianshan grassland ecosystem, which can be regarded as a typical representative of the mountain grasslands in Xinjiang. Eddy Covariance (EC) was used to continuously observe Xinjiang’s Middle Tianshan grassland ecosystem during the 2018 growing season. The results showed significant daily and monthly variations in net ecosystem exchange (NEE), gross primary productivity (GPP), and ecosystem respiration (Reco). On a daily scale, there was a net uptake of CO 2 during the day and a net release during the night. The grassland was a carbon sink from 6:00 to 18:00 and a carbon source for the rest of the day. At the monthly scale, June and July were carbon sinks, while the other months were carbon sources. The accumulated NEE, GPP, and Reco throughout the growing season were − 329.49 g C m − 2 , 779.04 g C m − 2 , and 449.55 g C m − 2 , respectively. On the half-hourly and daily scales, soil temperature (Ts) contributed the most to CO 2 fluxes and was the main factor influencing variations in CO 2 fluxes, while air temperature (Ta) was also highly correlated with CO 2 fluxes. CO 2 uptake in grassland ecosystems was strongest and peaked at soil temperatures of 25°C. As the air temperature reaches above 15℃, NEE gradually decreases while CO 2 uptake increases.