## 3 Results  
### Correlations between Carbon Fluxes and Environmental Factors  
We evaluated the consistency or decoupling of the forest sites by calculating the Spearman correlation coefficients of annual GPP and NEP for each site. And we calculated the average annual growth rates of GPP and NEP for each forest site. The correlations between annual GPP and NEP, as well as the average annual growth rates at selected forest sites, are shown in Table 2. The results showed that the annual GPP and NEP at 13 of the 14 sites were positively correlated, with 6 of the 13 sites having a significant positive correlation. In contrast, GPP was negatively correlated with NEP at the CA-Obs site, with a Spearman rank correlation coefficient (\(\rho\)) of \(-0.25\) (Table 2). This negative correlation indicated a decoupling of GPP and NEP at this forest site. The average annual growth rates of GPP and NEP at consistent forest sites followed the same trend, while at the decoupled site they showed an opposite trend, with growth rates of 2% and \(-4.9\%\), respectively (Table 2). This decoupling was closely related to changes in environmental conditions. Since NEP is the difference between GPP and RE, it is also closely related to the strength of RE. There was also further evidence of substantial site divergence, with significant differences in the response of GPP and NEP to environmental changes. The correlations among different environmental factors at annual and seasonal (spring, summer, and autumn) scales are shown in Tables 3-6, the interannual trends of carbon fluxes and environmental factors at different forest sites are shown in Table 11, and Figure 2 shows the relationships between environmental factors that led to consistent or decoupled trends in annual GPP and NEP. The results showed that when temperature and precipitation displayed significantly opposite trends at annual, spring, summer, and autumn time scales (Tables 3-6), there were consistent trends in GPP and NEP. Moreover, the inter-annual trends in temperature and precipitation maintained a synchronous relationship during these times (Table 11). This means that higher temperatures are usually accompanied by less precipitation. Additionally, there were consistent trends in GPP and NEP when TA\({}_{\text{MAM}}\) had the same trend as VPD\({}_{\text{MAM}}\), SW\({}_{\text{MAM}}\) had the same trend as VPD\({}_{\text{MAM}}\), TA\({}_{\text{JJA}}\) had the same trend as SW\({}_{\text{JJA}}\), and TA\({}_{\text{JJA}}\) had the same trend as VPD\({}_{\text{JJA}}\) (Table 11). In other words, their Spearman correlation coefficients were positive (Tables 4 and 5). Similarly, when TA\({}_{\text{SON}}\) had the same trend as VPD\({}_{\text{SON}}\) (Table 6), there were also consistent trends in GPP and NEP. This suggests that the alignment of these environmental variables may lead to a more synchronized response between GPP and NEP. The relationship between GPP and NEP in this ecosystem no longer maintained the same synchronous changes, and decoupling occurred under specific conditions involving temperature, SW, and VPD (Figure 2). Specifically, decoupling occurred when VPD\({}_{\text{MAM}}\) was significantly negatively correlated with both TA\({}_{\text{MAM}}\) and SW\({}_{\text{MAM}}\) (Table 4). Additionally, decoupling was noted when TA\({}_{\text{JJA}}\) was negatively correlated with both SW\({}_{\text{JJA}}\) and VPD\({}_{\text{JJA}}\) (Table 5). Also, in the decoupled site, inter-annual trends in VPD\({}_{\text{MAM}}\) were not synchronized with both TA\({}_{\text{MAM}}\) and SW\({}_{\text{MAM}}\) (Table 11). And correlations between environmental factors at the decoupled site were weak and non-significant. This suggests that the synchronization of carbon flux processes is highly sensitive to specific environmental stressors, especially those related to moisture availability and atmospheric dryness. Such decoupling highlights the complexity of ecosystem carbon dynamics and can lead to alterations in ecosystem carbon cycling processes.