## 1 Introduction  
Terrestrial plants fix carbon dioxide into the total amount of organic compounds through photosynthesis, which is called the total vegetation primary productivity or gross primary productivity (GPP). Terrestrial ecosystems are the largest carbon sink and the basis of food, fiber, and wood production [1]. The blade is an important medium for carbon sequestration in the atmosphere and on land. The terrestrial carbon sequestration capacity depends primarily on vegetation type, coverage, leaf area, and abundance. Leaf area index (LAI) is defined as the total leaf surface area per unit area. It is related to climate and plant function types and reflects the growth status of vegetation in the natural environment. LAI is sensitive to fertility, tree age, and management and is an important vegetation structure parameter [2]. Long-term monitoring of LAI and GPP can provide reference on the growth status of vegetation and the fixation capacity of the organic carbon in the natural environment in a study area. Regarding the methods of monitoring ecosystems, field sampling is a more accurate ecological detection method. Through in-depth field investigations, the regional and national ecological parameters can be better estimated [3]. The eddy covariance (EC) technique provides the CO\({}_{2}\) flux within a few kilometers of the flux tower. It is the best method for continuous measurement of the net ecosystem exchange, which can be used to calculate the GPP by subtracting the simulated ecosystem respiration components [4; 5]. The rapid development of remote sensing techniques has resulted in the ability to obtain continuous and consistent observations of large areas of vegetation, which has facilitated their broad application in monitoring and predicting vegetation dynamics [6; 7]. Multiple long-term vegetation remote sensing products have been developed using different methods, for example, the Advanced Very High Resolution Radiometer (AVHRR) series [8], Global Land Surface Satellite (GLASS) series [9], and Moderate Resolution Imaging Spectroradiometer (MODIS) series [10]. These remote sensing products can represent the spatiotemporal variation characteristics of vegetation well and have become an important tool for studying the human living environment and the Earth. China has a diverse ecological composition with a complex relationship between man and land [11]. Since the 2000s, to cope with the loss and degradation of natural ecosystems and strengthen the construction of ecological civilization, several large-scale ecosystem restoration projects have been implemented in China [12; 13]. Moreover, China has set the goal of reaching its carbon peak by 2030 and becoming carbon neutral by 2060. Therefore, in the field of sustainable development, the clarification of the ecological change pattern of the related system services has become an important issue in addition to achieving carbon neutrality and carbon peak on schedule. In recent years, scholars have extensively researched the spatio-temporal variation characteristics of LAI and GPP and their influencing factors. [PERSON] et al. show that LAI in China's Three Norths region has increased significantly in recent years [14]. [PERSON] et al. found that urban expansion in southwestern China partially offset afforestation-driven GPP growth [15]. [PERSON] et al. found that the project of returning cropland to forest-grassland has enabled southern China to achieve carbon benefits [16]. However, these studies in China have mostly focused on a certain region, and the contribution of different regions and provinces to changes in LAI and GPP at the national level has not been reported. The results of previous research show that changes in vegetation structure and function are mainly affected by two aspects: human activities [17] and climate change [18].