###### Abstract  
The gross primary productivity (GPP) of vegetation stores atmospheric carbon dioxide as organic compounds through photosynthesis. Its spatial heterogeneity is primarily influenced by the carbon uptake period (CUP) and maximum photosynthetic productivity (GPP\({}_{\max}\)). Grassland, cropland, and forest are crucial components of China's terrestrial ecosystems and are strongly influenced by the seasonal climate. However, it remains unclear whether the evolutionary characteristics of GPP are attributable to physiology or phenology. In this study, terrestrial ecosystem models and remote sensing observations of multi-source GPP data were utilized to quantitatively analyze the spatio-temporal dynamics from 1982 to 2018. We found that GPP exhibited a significant upward trend in most areas of China's terrestrial ecosystems over the past four decades. Over 60% of Chinese grassland and over 50% of its cropland and forest exhibited a positive growth trend. The average annual GPP growth rates were 0.23 to 3.16 g C m\({}^{-2}\) year\({}^{-1}\) for grassland, 0.40 to 7.32 g C m\({}^{-2}\) year\({}^{-1}\) for cropland, and 0.67 to 7.81 g C m\({}^{-2}\) year\({}^{-1}\) for forest. GPP\({}_{\max}\) also indicated that the overall growth rate was above 1 g C m\({}^{-2}\) year\({}^{-1}\) in most regions of China. The spatial trend pattern of GPP\({}_{\max}\) closely mirrored that of GPP, although local vegetation dynamics remain uncertain. The partial correlation analysis results indicated that GPP\({}_{\max}\) controlled the interannual GPP changes in most of the terrestrial ecosystems in China. This is particularly evident in grassland, where more than 99% of the interannual variation in GPP is controlled by GPP\({}_{\max}\). In the context of rapid global change, our study provides an accurate assessment of the long-term dynamics of GPP and the factors that regulate interannual variability across China's terrestrial ecosystems. This is helpful for estimating and predicting the carbon budget of China's terrestrial ecosystems. g 2024 14 August 2024 22 August 202  
period (CUP) and the maximum photosynthetic productivity (GPP\({}_{\text{max}}\)) [3]. Specifically, an earlier start of the growing season (SOS) and a later end of the growing season (EOS) can extend the duration of the growing season or alter the timing of photosynthesis activity [4; 5], elucidating the spatial heterogeneity of GPP\({}_{\text{annual}}\) from a mechanistic perspective. Currently, plant phenology research, particularly focusing on SOS and EOS, has garnered widespread attention [3]. However, there are a limited number of studies focusing on GPP\({}_{\text{max}}\), a crucial factor in delineating ecosystem GPP capacity and influencing the seasonal patterns of atmospheric CO\({}_{2}\) concentrations, especially for terrestrial ecosystems of China with significant seasonality. Grassland, cropland, and forest are crucial components of terrestrial ecosystems, playing a vital role in regulating greenhouse gas cycling and maintaining ecosystems' carbon balance [6]. According to the bulletin of the third major national land survey released by the State Forestry and Grassland Administration [7], grassland, cropland, and forest in China collectively occupy 85% of the total land area, constituting the main components of the terrestrial ecosystems. Given that most parts of China lie within the monsoon zone, with significant seasonal climate variations, China's terrestrial ecosystems exhibits high sensitivity to both climate change and human-induced disturbances [8]. Hence, the precise evaluation of spatial and temporal variations, coupled with an analysis of interannual GPP variability mechanisms in China's terrestrial ecosystems under the backdrop of climate change, can facilitate the estimation and prediction of carbon balance of these terrestrial ecosystems.