## 4 Discussion
### Simulations under Future Climate Scenarios  
The simulation results show that from 2020 to 2100, the GPP values at both sites increased. The carbon uptake rates in tundra vary greatly under different climate scenarios. Climate warming at high latitudes can alleviate the effects of cold stress on vegetation growth [49] and thus promote vegetation growth [50]. With the increase in temperature, precipitation, and atmospheric CO\({}_{2}\) content, the Arctic will show a \"greening\" trend [51]. A previous study based on the CoupModel simulation in the Greater Khingan Mountains permafrost region also suggested that the GPP and carbon uptake tended to increase in a warming climate. We found that the maximum GPP values appeared under the SSP5-8.5 scenario, and the minimum values appeared under the SSP1-2.6 scenario. However, the carbon uptake rates showed much lower increasing rates. Under the SSP5-8.5 scenario, the GPP values are the highest, due to this prediction of higher greenhouse gas emissions and temperature rise, which typically enhances the growth rate and biomass of vegetation in certain regions, particularly in temperate and high-latitude areas [52]. In contrast, the SSP1-2.6 scenario forecasts more moderate greenhouse gas emissions and climate change, resulting in relatively lower GPP values. However, despite the increase in GPP under certain scenarios, the rate of carbon sequestration is relatively slow. This is partly the elevated concentrations of greenhouse gases and rising temperatures accelerate the thawing of permafrost. As permafrost thaws, the previously frozen organic is released and decomposed through microbial activity, promoting soil respiration [53; 54]. Soil respiration,the process by which soil microorganisms decompose organic matter and release carbon dioxide, is enhanced by these conditions, leading to the release of carbon from the soil into the atmosphere, thereby offsetting some of the carbon fixed by the increased photosynthesis due to vegetation growth [55]. In summary, while climate warming may promote vegetation growth and primary productivity in the short term, the accelerated thawing of permafrost and the increase in soil respiration could lead to a future where carbon sequestration in the Arctic region may not significantly increase. In the future scenario, the NEE value simulated using the model shows a decreasing trend, which means that the carbon sequestration capacity of the ATQ tundra site and PRR needle leaf forest site in the Arctic region will increase, and the carbon sequestration capacity of PRR site will be stronger and the vegetation growth condition will be better. Under the future warming scenario, the net vegetation carbon exchange of tundra sites is larger than that of forest sites, while the net soil carbon exchange is smaller than that of forest sites. The decomposition of soil organic matter is positively correlated with soil temperature, and the net soil carbon exchange rate will accelerate with future temperature increases. In the Arctic ecosystem, the net soil carbon exchange rate of forest sites is greater than that of tundra sites. In the SSP1-2.6 scenario, the rate of carbon sequestration in coniferous forest sites is the fastest, likely reflecting the relatively mild climate conditions of this scenario that favor carbon fixation. Overall, the carbon exchange at PRR coniferous forest sites is higher than that at ATQ permafrost sites, possibly due to the greater biomass and carbon storage capacity of coniferous forests [56]. Although carbon exchange is higher under the SSP5-8.5 scenario than under SSP1-2.6, the transformation rate is quicker in the SSP1-2.6 scenario, indicating that ecosystems under scenarios with lower greenhouse gas emissions adapt and respond more rapidly to climate change.