## 3 Results
### Relative Contributions of Different Environmental Factors to the Annual Carbon Fluxes  
The relative contributions of different environmental factors to the annual carbon fluxes were investigated using the PLS method, with the results for the forest sites with consistent and decoupled trends in GPP and NEP shown in Figures 5 and 6, respectively. At forest sites with consistent trends in GPP and NEP, annual and seasonal temperatures contributed much more to carbon fluxes than the other three environmental factors, and spring and autumn temperatures contributed more than 50% to GPP and NEP (Figure 5b,d). Precipitation contributed more to NEP than to GPP and RE, while SW contributed more to RE than to GPP and NEP, and VPD contributed the least, especially for NEP, which is only 5%-8% (Figure 5). TA\({}_{\text{SON}}\) contributed more to NEP, accounting for 60% (Figure 5d), suggesting that autumn temperature is an important factor in promoting carbon sequestration. These findings suggest that temperature and precipitation were the key environmental factors affecting forest ecosystems in sites with consistent trends in GPP and NEP, while SW also had a substantial influence on GPP and RE.  
Figure 5: Relative contributions of annual and seasonal environmental factors to annual carbon fluxes at forest sites with consistent trends in GPP and NEP. (**a**) represents year, (**b**) represents spring (March, April, and May), (**c**) represents summer (June, July, and August), and (**d**) represents autumn (September, October, and November). The orange, green, purple, and yellow bars represent temperature, SW, VPD, and precipitation, respectively.  
At the forest site where GPP and NEP were decoupled, the contributions of temperature and SW to carbon fluxes were comparable at different time scales (Figure 6). The contributions of \(\mathrm{P_{year}}\) and \(\mathrm{P_{MAM}}\) to carbon fluxes were almost negligible (Figure 6a,b). \(\mathrm{VPD_{year}}\) contributed significantly more to GPP and RE than other environmental factors, at 66% and 53%, respectively (Figure 6a). \(\mathrm{P_{JJA}}\) was more important to NEP, accounting for 43%, offsetting the negative effect of summer high temperatures, and \(\mathrm{VPD_{JJA}}\) was also more important to GPP and RE than other environmental factors, accounting for 46% and 38%, respectively (Figure 6c). In autumn, the four environmental factors contributed equally to all carbon fluxes (Figure 6d). These observations suggest that at the forest site where GPP and NEP were decoupled, the dominance of the influence of \(\mathrm{VPD_{year}}\) and \(\mathrm{VPD_{JJA}}\) on GPP indicated the importance of annual and seasonal climate change on ecosystem photosynthesis, while \(\mathrm{P_{JJA}}\) and \(\mathrm{SW_{MAM}}\) dominated NEP, further highlighting the importance of seasonal climatic elements on NEP processes.  
At forest sites with consistent trends in GPP and NEP, the changes in the annual carbon fluxes were primarily driven by temperature, followed by precipitation, SW, and VPD. In contrast, at the forest site with decoupled GPP and NEP, \(\mathrm{VPD_{year}}\), \(\mathrm{VPD_{JJA}}\), and \(\mathrm{P_{JJA}}\) were the dominant factors, followed by the effects of temperature and SW.  
Figure 6: Relative contributions of annual and seasonal environmental factors to annual carbon fluxes at the forest site with a decoupled trend in GPP and NEP. (**a**) represents year, (**b**) represents spring (March, April, and May), (**c**) represents summer (June, July, and August), and (**d**) represents autumn (September, October, and November). The orange, green, purple, and yellow bars represent temperature, SW, VPD, and precipitation, respectively.