## 1 Introduction  
Climate change is substantially affecting vegetation physiological activities in the boreal ecosystem [1, 2]. Vegetation phenology and productivity are two kinds of biological parameters highly sensitive to climate dynamics, and are widely employed to elucidate the response of terrestrial ecosystems to climate changes [3]. Both satellite observations and atmospheric reanalysis data indicate that the boreal terrestrial ecosystem has warmed at a rate 2.5-2.8 times the global average in the past two decades [4]. With the ongoing amplified warming in this region, shifts in GPP could have profound implications for carbon cycling and climate feedback mechanisms [5]. The gross primary productivity (GPP), representing the quantity of carbon absorbed by vegetation via photosynthesis [6], plays a pivotal role in regulating the carbon cycle [7]. Under the influence of the amplified warming at high latitudes of the Northern Hemisphere in recent years [4, 8], boreal vegetation productivity was responding dramatically. However, recent studies indicate two different understandings; some scholars suggest that there has been a stagnation or slowdown in GPP increase during recent decades [9, 10], while other scholars argue that the GPP has continued to increase over the past two decades [11]. These discrepancies are further compounded by substantial differences among different GPP models in their representation of inter-annual variability and long-term trends [12; 13]. There is still no consensus on the GPP changes in boreal ecosystems. Similarly, the spatiotemporal changes in boreal vegetation phenology have remained uncertain over the past four decades. This uncertainty arises from several factors, including inconsistencies in long-term satellite products [14; 15], variations in phenology retrieval algorithms [16; 17; 18], and differences in study periods [19; 20]. As a result, there is considerable divergence in the reported trends. Based on satellite observations and in situ measurements, various efforts were taken to determine the changes in boreal vegetation phenology [14; 15; 17; 19; 20; 21]. The reported trends of advanced SOS and delayed EOS exhibit substantial variability, ranging from 1.4 days to 4.0 days per decade [22; 23; 24] and 1.8 days to 3.3 days per decade [25; 26], respectively. Some studies found that the extension of vegetation phenology in the boreal vegetation has slowed down [18] and even reversed in recent years [27], while other studies indicated that the speed of SOS advancement and EOS delay from 2002 to 2012 was even faster than that from 1982 to 1992 [28]. Despite these uncertainties, there is a general consensus on the trends of earlier SOS in spring, later EOS in autumn, and consequently, an increased length of growing season (LOS) [27; 29]. Under the influence of climate changes, vegetation phenology in boreal territorial ecosystems was responding more pronounced than in other regions [30; 31; 32]. Vegetation phenology shapes the duration of canopy photosynthesis [33]. The two critical phenology metrics, the start (SOS) and end (EOS) of the growing season, representing the beginning and end of the vegetation photosynthesis activity, together determine the length of the growing season (LOS) and the annual GPP [34; 35]. To assess the impact of vegetation phenology on GPP, a variety of methodologies are frequently employed. Statistical approaches, including linear regression, generalized linear models, and structural equation modeling [36], are utilized to quantify the relationship between phenological changes and GPP variations. Ecological process models, such as CASA and BIOME-BGC, are applied to simulate the interactions between phenology and GPP under diverse climate scenarios [37; 38]. Additionally, the integration of remote sensing observation and climate variables provides a holistic framework for assessing the synergistic impacts of climate factors and phenological shifts on GPP variations [39].