# Characteristics of Carbon Fluxes and Their Environmental Control in Chenhu Wetland, China
## 3 Results and Discussion
### Relationships Between NEE and Some Environmental Parameters
However, the elevated VPD induces partial stomatal closure in the leaves of wetland vegetation, which subsequently results in a decrease in \(\alpha\) and hinders the overall photosynthetic process in these plants [54]. Since September 2022, the Chenhu wetland has been subjected to a prolonged drought. This extended period of low precipitation, combined with elevated VPD, has led to a significant inhibition of photosynthesis, resulting in the lowest recorded values of P\({}_{\text{max}}\), \(\alpha\), and R\({}_{\text{eco,day}}\). An analysis of the response characteristics of daytime NEE to PAR across varying VPD levels in the Chenhu wetland indicates that the optimal VPD range for plant photosynthesis in this region is between 0.5 and 1.5 kPa. Within this range, the correlation between daytime NEE and PAR is significantly enhanced, and both P\({}_{\text{max}}\) and \(\alpha\) exhibit elevated values. Temperature serves as the primary environmental determinant influencing ecosystem respiration. The relationship between T\({}_{\text{a}}\) and CO\({}_{2}\) flux during both the growing and non-growing seasons is depicted in Figure 9. It is evident that CO\({}_{2}\) flux exhibits an exponential increase in response to rising temperatures. However, the data points presented in Figure 9 demonstrate considerable variability due to the influence of additional environmental factors. During the non-growing season, T\({}_{\text{a}}\) accounts for 26.56% of the variability in CO \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Month**} & \multirow{2}{*}{\(\alpha\)} & **P\({}_{\text{max}}\)** & **R\({}_{\text{eco,day}}\)** & **Number of** & \multirow{2}{*}{\(R^{2}\)} & \multirow{2}{*}{\(p\)} \\  & **(\(\mu\text{molCO}_{2}\)\(\mu\text{mol}^{-1}\))** & **(\(\mu\text{molCO}_{2}\)\(\cdot\)m\({}^{-2}\).s\({}^{-1}\))** & **(\(\mu\text{molCO}_{2}\)\(\cdot\)m\({}^{-2}\).s\({}^{-1}\))** & **Samples (\(n\))** & \\ \hline April & 0.0757 & 14.73 & 3.80 & 773 & 0.25 & \textless{}0.01 \\ May & 0.0544 & 21.51 & 3.46 & 863 & 0.47 & \textless{}0.01 \\ June & 0.0479 & 16.22 & 2.77 & 865 & 0.51 & \textless{}0.01 \\ July & 0.0286 & 19.31 & 3.38 & 895 & 0.65 & \textless{}0.01 \\ August & 0.0136 & 21.92 & 3.10 & 837 & 0.58 & \textless{}0.01 \\ September & 0.0186 & 10.10 & 2.05 & 761 & 0.36 & \textless{}0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulated parameters of light response curve in the growth season. Figure 8: Scatter plots of daytime NEE against PAR under different VPD during the growth season. The fitting results and correlation coefficients between daytime NEE and PAR are also shown. flux, indicating its significant role as a controlling factor during this period. Conversely, in the growing season, T\({}_{\rm a}\) explains only 7.61% of the variability in nighttime CO\({}_{2}\) flux, suggesting that other environmental factors exert a more pronounced influence during this time. Furthermore, temperature primarily impacts plant photosynthesis by modulating the activity of leaf enzymes ([PERSON] _et al._, 2018). During the non-growing season, lower temperatures were observed, and a strong correlation was established between CO\({}_{2}\) flux and T\({}_{\rm a}\). This suggests that at reduced temperatures, an increase in T\({}_{\rm a}\) can enhance the enzymatic activity of plant leaves, resulting in a greater rate of plant respiration compared to photosynthesis, thereby leading to an increase in CO\({}_{2}\) emissions. The sensitivity coefficient (Q\({}_{10}\)) for T\({}_{\rm a}\) during the night in both the growing and non-growing seasons was recorded at 1.27 and 1.75, respectively. These values are consistent with findings from previous studies conducted on wetland ecosystems, such as the eastern Chongming tidal flat wetland ([PERSON] _et al._, 2018) and the Yellow River Delta ([PERSON] _et al._, 2018), indicating that the NEE of the Chenhu wetland ecosystem exhibits significant responsiveness to fluctuations in temperature.