## 1 Introduction  
Gross primary production (GPP), the summation of carbon fixed by plants during photosynthesis, is of great significance in a variety of ecosystem functions such as growth and respiration [1]. As the main driving force of terrestrial carbon sequestration, GPP has a profound impact on global carbon balance and can partially regulate the atmospheric carbon dioxide (CO\({}_{2}\)) emissions from fossil fuel consumption [2, 3]. Meanwhile, GPP is a key element for ecological regulatory behaviors and an important indicator of ecosystem health [4]. It affects food, fiber, energy, and provides ecosystem services that alleviate the increasingly serious greenhouse effects [5; 6]. Characterizing the spatiotemporal variations and trends of GPP is vital for a deeper understanding of the carbon cycle between terrestrial ecosystems and the atmosphere [7]. Due to the profound impact of GPP on terrestrial vegetation, its variations and trends reflect ecological environmental quality [8]. More importantly, GPP dynamics integrate geochemical, ecological and human impacts into terrestrial ecosystems. As a result, the continuous monitoring of GPP will enhance our ability to explain the complex mechanisms of the biosphere [9]. However, since current GPP products rely on assumptions and are based on different estimation models, there is not a set of GPP products that can perform better consistently in different ecosystems and external conditions. As a result, the variations and trends obtained from different GPP products are often differential [10], and thus the research scope of GPP dynamics is limited to the local scale. In previous studies, [PERSON] et al. [11] analyzed the GPP dynamics in China's Three-North Region over the last forty years by comparing the trend differences and the underlying causes in four sub-regions. [PERSON] et al. [12] evaluated the spatiotemporal pattern of the phenological index and the GPP from 2001 to 2017 in the Yungui Plateau, and explored its response to droughts. The aforementioned research has improved the understanding of GPP dynamics in specific areas to varying degrees. However, the external conditions of these study areas were relatively monotonic, i.e., they were at a local scale. The climatic and hydrothermal environments of a study area which can be called large scale are generally not unified, and the research results obtained from single GPP products are also unconvincing [13]. With that being said, local-scale analysis is not conducive to understanding the macro patterns of vegetation productivity, and it is therefore urgent to investigate the variations and trends of GPP at a large scale. At the same time, in order to ensure the accuracy of the analysis results, multiple sets of GPP products should be used to verify each other. Climate change affects ecosystem productivity by changing the absorption of light, heat, and water during plant growth and development [14; 15]. The effects of climate factors on vegetation productivity have significant spatiotemporal differences [16], and the response of the productivity of different vegetation types to climate factors is also inconsistent [17]. In the past few decades, the global climate has experienced major changes represented by frequent extreme weather catastrophes and continuous warming [18]. Ecosystems and terrestrial carbon sinks will be significantly affected by climatic variation. For example, the plant productivity of Europe has decreased by about 30% because of droughts and heat waves [19]. On the other hand, GPP is substantially impacted by human activities [20]. Although a massive implementation of afforestation is conducive to the restoration of vegetation, which could increase GPP, population growth and rapid economic development have intensified urbanization and undermined the balance of terrestrial ecosystems. These human interventions have a significant impact on the formation of GPP dynamics [21; 22].