###### Abstract  
Carbon uptake of vegetation is controlled by phenology and photosynthetic carbon uptake capacity. However, our knowledge of the seasonal responses of vegetation productivity to phenological and physiological changes in alpine ecosystems is still weak. In this study, we quantified the spatio-temporal variations of vegetation phenology and gross primary productivity (GPP) across the source region of the Yellow River (SRYR) by analyzing MODIS-derived vegetation phenology and GPP from 2001 to 2019, and explored how vegetation phenology and maximum carbon uptake capacity (GPP\({}_{\text{max}}\)) affected seasonal GPP over the region. Our results showed that the SRYR experienced significantly advanced trends (\(p<0.05\)) for both start (SOS) and peak (POS) of the growing season from 2001 to 2019. Spring GPP (GPP\({}_{\text{SP}}\)) had a significantly increasing trend (\(p<0.01\)), and the earlier SOS had obvious positive effects on GPP\({}_{\text{SP}}\). Summer GPP (GPP\({}_{\text{Sum}}\)) was significantly and negatively correlated to POS (\(p<0.05\)). In addition, GPP\({}_{\text{max}}\) had a significant and positive correlation with GPP\({}_{\text{Sum}}\) and GPP\({}_{\text{am}}\) (\(p<0.01\)), respectively. It was found that an earlier spring-summer phenology and higher photosynthetic peak enhanced the photosynthetic efficiency of vegetation in spring and summer and altered the seasonal patterns of vegetation productivity in the SRYR under warming and wetting climates. This study indicated that not only spring and autumn phenology but also summer phenology and maximum carbon uptake capacity should be regarded as crucial indicators regulating the carbon uptake process in alpine ecosystems. This research provides important information about how changes in phenology affect vegetation productivity in alpine ecosystems under global climate warming. alpine ecosystems; phenology; photosynthetic peak; gross primary productivity 2024 16 180 189 2024 27 April 20  
climatic zone and ecosystem types is essential to accurate assessments of the spatial and temporal variations in annual GPP at regional and global scales [11; 12; 13]. Shifts of vegetation phenology due to climate changes can affect vegetation productivity by affecting the process of carbon uptake [14; 15; 16; 17]. Most of previous studies on vegetation phenology have demonstrated that the start of the growing season (SOS) and the end of the growing season (EOS) have, respectively, advanced and delayed trends under global warming [18; 19; 20]. [PERSON] et al. [21] found that earlier SOS and later EOS led to an extension of the length of growing season (LOS) in the Tibetan Plateau, resulting in an increase of the gross primary productivity of vegetation. The spatio-temporal responses of vegetation productivity to phenology may differ among various climatic zones and ecosystem types [22]. [PERSON] et al. [23] reported that the increase of vegetation gross primary productivity in the eastern Tibetan Plateau was mainly due to the advance of the SOS rather than the delay of the EOS, whereas [PERSON] et al. [10] found that the delay of the EOS remarkably enhanced the GPP over the period from September to October for broadleaf forests in east China. In addition, a delayed EOS may not lead to a substantial increase of GPP due to weak photosynthetic efficiency and the limited ability of organic matter accumulation in autumn [24; 25]. Most studies have focused on the effects of phenological factors (SOS, EOS and LOS) on vegetation productivity at the annual scale [13]. However, it is still unclear how phenology affects vegetation productivity at the seasonal scale, especially for the peak of growing season. Peak of growing season (POS) represents the timing of the seasonal peak canopy structure, which reflects the ability of terrestrial ecosystem productivity [26] and is an important phenology indicator for the carbon cycle of terrestrial ecosystems [27].