## 1 Introduction  
Carbon dioxide (CO\({}_{2}\)) fluxes in terrestrial ecosystems play a crucial role in the study of the global carbon cycle and carbon balance. Changes in land-air carbon exchange can cause significant fluctuations in CO\({}_{2}\) concentrations, which have important implications for global climate change [1, 2]. Grassland ecosystems, as an important component of global terrestrial ecosystems, play a crucial role in the carbon cycle of global terrestrial ecosystems [3,4]. Among all of the terrestrial ecosystems worldwide, grassland ecosystems have the second highest carbon stock after forest ecosystems, reaching 308 Pg C. Simultaneously, grasslands play a critical role in maintaining both the global carbon cycle and the structural stability of ecosystems [5]. Many scholars have explored the carbon sequestration capacity of grassland ecosystems through various methods such as eddy correlation techniques [6], experiments on the control of temperature and precipitation [7,8], as well as the coupling of remote sensing and models [9]. However, at present, most of the research on CO\({}_{2}\) fluxes in grassland ecosystems in China is focused on desert grasslands, typical grasslands, and alpine grasslands [10, 11, 12]. There is uncertainty in accurately estimating carbon flux in mountain grasslands. Xinjiang has abundant grassland resources, covering a total area of 572,590 km\({}^{2}\) and a net area of 480,070 km\({}^{2}\), accounting for 34.68% of Xinjiang's total area and 14.50% of China's total area. Furthermore, the natural grasslands in Xinjiang are mainly distributed in mountainous areas, which account for 58% of Xinjiang's total grassland area and are the primary location for Xinjiang's grassland animal husbandry operations [13]. Simultaneously, the diversity of grassland ecosystems, types, and species creates favorable conditions for mitigating the natural shortcomings of grasslands and also provides opportunities for the development of efficient livestock industries [14]. Global climate change and regional human activities have significantly influenced the carbon cycling processes in the Middle Tien Shan grassland ecosystem [15]. Currently, research on carbon fluxes in the Tien Shan region of Xinjiang mainly focuses on studying soil carbon stocks in grasslands on the northern slopes of the Tien Shan Mountains, with a lack of studies on ecosystem carbon fluxes using the eddy covariance (EC) system [16]. Moreover, the grassland vegetation in the Tien Shan Mountains of Xinjiang exhibits distinct vertical and horizontal zonal distribution patterns. Furthermore, various types of grasslands can be found in the Tien Shan Mountains, including mountain desert, mountain desert grassland, mountain grassland, mountain meadow grassland, mountain meadow and alpine meadow grassland. Meanwhile, these representative grassland types play a crucial role in maintaining ecological balance and protecting biodiversity, serving as natural green barriers for the sustainable utilization of desert oases. The EC system is a technique that can monitor carbon fluxes over an extended period and is widely used in various ecosystem areas [17, 18, 19]. Therefore, utilizing the EC system to measure changes in carbon fluxes in the Middle Tien Shan grassland ecosystem and to investigate their relationship with environmental factors not only addresses the deficiency of carbon flux data in this ecosystem but also provides a scientific basis for studying the carbon cycle in grassland ecosystems throughout the region and even in China. Remote sensing technology enables the transition from site-specific research to regional scales. The development of satellite data for carbon monitoring has provided possibilities for this research. GOSAT and OCO, as the main greenhouse gas satellites, are widely used in the study of carbon flux spatiotemporal variations [20, 21, 22, 23].