## 5 Conclusions  
This study uncovered that phenological shifts increasingly drive productivity changes in boreal ecosystems. The analysis investigated long-term changes in boreal vegetation phenology and GPP over the period 1982-2018, focusing on the boreal terrestrial ecosystem. Our results revealed divergent trends in vegetation phenology and GPP across two distinct periods (P1: 1982-2000, P2: 2001-2018). Forest ecosystem growing season extension decelerated in the recent period, while grass and shrub ecosystem phenology, particularly in high-latitude regions, exhibited accelerated lengthening. The contribution of phenology extension to GPP changes, quantified with the RIE metric, shows a 22% increase during P2, with the most pronounced increment observed in northern Siberia.  
These findings enhance our understanding of the crucial role that phenology plays in regulating boreal ecosystem productivity under a warming climate. The prolongation of the growing season allowed vegetation to enlarge photosynthetic activity, mitigating the atmospheric drought-induced saturation of photosynthetic capacity and the slowdown of GPP increase in summer. Quantifying the impact of phenology extension on GPP increment with the RIE metric reveals how vegetation phenology shifts, particularly in high-latitude regions, were reshaping boreal ecosystem functions. These insights are vital for understanding the complex feedback mechanisms between climate and vegetation in these rapidly changing ecosystems. There are still some limitations in our study. The use of remote sensing data with moderate spatial resolution may overlook finer-scale variations in vegetation dynamics. Additionally, the analysis did not incorporate local environmental factors, such as topography or microclimates, which could affect phenological shifts and GPP patterns.  
In conclusion, this study underscores the growing importance of phenological shifts in shaping boreal ecosystem productivity under amplified warming climates. By providing new insights into the role of phenology in regulating photosynthetic activity and GPP, the research offers a deeper understanding of how climate change may alter carbon dynamics in boreal regions in the future.  
Conceptualization, Y.C.; Data curation, M.Y. and B.R.; Methodology, M.Y. and Y.C.; Resources, Y.C.; Writing--original draft, M.Y.; Writing--review and editing, Y.C. and J.T. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by the National Key Research and Development Program of China, grant number 2023 YFD2201702-3, and the National Natural Science Foundation of China, grant number 42330507.  
**Data Availability Statement:** The GLASS GPP product is freely available from the National Earth System Science Data Center ([[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn)), accessed on 17 June 2022). The global land cover product MCD12C1, with a 0.05\({}^{\circ}\) spatial resolution, was obtained from NASA Land Processes Distributed Active Archive Centre ([[https://lpdaac.usgs.gov/products/mcd12c1v061](https://lpdaac.usgs.gov/products/mcd12c1v061)]([https://lpdaac.usgs.gov/products/mcd12c1v061](https://lpdaac.usgs.gov/products/mcd12c1v061)), accessed on 20 August 2023).  
**Acknowledgments:** The authors acknowledge the data support from the National Earth System Science Data Center. ([[https://www.geodata.cn](https://www.geodata.cn)]([https://www.geodata.cn](https://www.geodata.cn)), accessed on 17 June 2022).  
**Conflicts of Interest:** The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.