###### Abstract  
The ecosystem's gross primary productivity (GPP) and greenness, as indicated by the normalized difference vegetation index (NDVI), are both essential ecological indicators used to evaluate how ecosystems responded to climate variability. However, the relationships between NDVI and GPP under the influence of drying and wetting and its characteristics along aridity (AI) gradients were not yet fully understood. In this study, we investigated the relationships of the NDVI-GPP (i.e., the strength of the coupling and the sensitivity, as quantified by the coefficient of determination (R\({}^{2}\)) and slope of the linear regression, respectively) along the aridity gradients during the growing season from 1982 to 2018 in China. The results show that the coupling between NDVI and GPP was stronger (i.e., high R\({}^{2}\)) in semi-arid regions (0.24) compared to humid and hyper-humid regions (R\({}^{2}\) values were 0.11). For different plant functional types (PFTs), decoupling occurred in ENF with a determination coefficient value (R\({}^{2}\)) of 0.04, whereas GRA shows a higher coupling with an R\({}^{2}\) of 0.20. The coupling trend experienced a shift in semi-arid regions, characterized by an aridity index (AI) ranging from 0.20 to 0.50. Additionally, the sensitivity of GPP to NDVI also decreased with increasing aridity. The slope values were 0.19, 0.21, 0.24, 0.20, 0.11, and 0.11 in hyper-arid, arid, semi-arid, dry sub-humid, humid, and hyper-humid, respectively. What is more, asynchronous changes in vegetation productivity and greenness can be detected by capturing the inter-annual variability (IAV) of NDVI and GPP. The IAV of GPP steadily decreased with the aridity gradients, while the IAV of NDVI present fluctuated, suggesting that NDVI was more variable than GPP under the influence of drying and wetting conditions. Our study suggests that there may be a stronger trade-off between ecosystem greenness and photosynthesis in more humid areas. g 2024 16 2024 11 October 2024 9 November 2024 11 November 2024 14 November 2024 14 November 2024 11 October 2024 11 October 2024 9 November 2024 11 November 2024  
reduces vegetation productivity and weakens carbon cycles [6]. Consequently, regional terrestrial ecosystems may transition from being carbon sinks to carbon sources [7; 8]. Gross primary production (GPP) and vegetation indices (VIs) play a crucial role in regulating climate change and mediating vegetation-land-atmosphere interactions [9; 10; 11]. As the primary indicator of photosynthetic activity, GPP significantly contributes to global carbon sequestration [12; 13]. Simultaneously, various vegetation indices, including the leaf area index (LAI), enhanced vegetation index (EVI), and normalized difference vegetation index (NDVI), are used to monitor how vegetation greenness changes with the season, providing valuable insights into the seasonal patterns of GPP [14]. Both NDVI and EVI data products are sensitive indicators of leaf area and chlorophyll content. Unlike GPP and LAI, they are based purely on the radiometrically and geometrically corrected measurements made by satellites. MODIS EVI, in particular, provides a vegetation index that does not saturate at high chlorophyll situations and is less sensitive to atmospheric and soil contamination. Overall, satellite remote sensing technology provides a way to continuously monitor the greenness and productivity across wide areas [15]. Through this monitoring, a significant greening trend in vegetation area has been revealed since the 1980s, both in China and globally [16; 17; 18]. Ongoing greening has led to increased terrestrial ecosystem productivity [19; 20; 21], primarily due to the positive relationship between greenness and productivity [22; 23]. Vegetation productivity and greenness are also affected by hydrological climate change and aridity conditions and show a trend towards non-linear responses.