## 3 Results
### Responses of the Annual Carbon Fluxes to Environmental Changes
P\({}_{\text{year}}\) was significantly positively correlated with GPP (Figure 3a), indicating the importance of moisture in regulating carbon fluxes in forest ecosystems. SW\({}_{\text{year}}\) was weakly negatively correlated with GPP and significantly negatively correlated with RE (Figure 3a). In contrast, at the decoupled forest site, we observed that the effect of VPD\({}_{\text{year}}\) was significantly negatively correlated with GPP and RE, whereas this effect was a little weaker but also significantly negatively correlated at the forest sites with consistent trends in GPP and RE. This suggests that VPD plays a critical role in regulating the productivity of forest ecosystems (Figure 3). However, unlike the sites with a consistent trend, at the decoupled forest site, TA\({}_{\text{year}}\) had a non-significant negative correlation with GPP and RE, P\({}_{\text{year}}\) had a non-significant effect on GPP and RE, and SW\({}_{\text{year}}\) had a significant positive correlation with RE (Figure 3b). We also investigated the responses of annual carbon fluxes to seasonal (spring, summer, and autumn) environmental factors, with the results shown in Figure 4. At forest sites with consistent trends in GPP and NEP, TA\({}_{\text{MAM}}\) and TA\({}_{\text{JJA}}\) contributed significantly to GPP and RE, with PCs of 0.55-0.81 (Figure 4a,c). This suggested that an increase in spring and summer temperatures had a significant positive effect on increasing the GPP and RE in forest ecosystems. TA\({}_{\text{SON}}\) had a significant positive correlation with GPP (PC = 0.8) and almost no correlation with RE, suggesting that higher autumn temperatures contribute stronger to the increase in GPP. SW\({}_{\text{MAM}}\) had a more significant promoting effect on GPP (PC = 0.23), while SW\({}_{\text{JJA}}\) had strong inhibitory effects on GPP (PC = \(-\)0.69) (Figure 4a,c). SW\({}_{\text{MAM}}\), SW\({}_{\text{JJA}}\), and SW\({}_{\text{SON}}\) had strong inhibitory effects on RE with PCs of \(-\)0.7--0.41, which became significantly negatively correlated (Figure 4a,c,e). This indicated that SW\({}_{\text{MAM}}\) provided sufficient energy for photosynthesis and promoted the increase in GPP. In summer, when the radiation intensity is higher, excessive light may also cause photoinhibition, which further reduces GPP [36]. In addition, high radiation intensity may cause plants to close stomata to reduce water loss, which also reduces RE. Moreover, spring, summer, and autumn precipitation and VPD had a low correlation and minimal effect on both GPP and RE (Figure 4a,c,e). However, at the decoupled forest site, TA\({}_{\text{JJA}}\) and TA\({}_{\text{SON}}\) had a very weak contribution to carbon flux effects with correlation coefficients close to 0, but TA\({}_{\text{MAM}}\) became significantly positively correlated with GPP and RE (Figure 4b,d,f). SW\({}_{\text{MAM}}\) significantly promoted GPP and RE, with a stronger effect on RE (Figure 4b), while SW\({}_{\text{JJA}}\) and SW\({}_{\text{SON}}\) became significantly negatively correlated with GPP and RE (Figure 4d,f). This indicated that abundant sunlight positively promoted GPP in the early stages of plant growth in spring, but the trends of GPP and NEP changed and appeared to become decoupled due to the stronger effect of SW on RE. P\({}_{\text{MAM}}\) also contributed significantly to GPP and RE, and more strongly to RE (Figure 4b). P\({}_{\text{JJA}}\) had a significant negative correlation with GPP and RE (Figure 4d), while P\({}_{\text{SON}}\) had almost no correlation with either (Figure 4f). There was no significant correlation between VPD and GPP or RE in spring (Figure 4b). However, VPD\({}_{\text{JJA}}\) became significantly negatively correlated with GPP (Figure 4d), and VPD\({}_{\text{SON}}\) became significantly positively correlated with GPP (Figure 4f). These results suggest that the mechanism by which environmental conditions influence plant RE is complex.