## 3 Results  
Effects of CO\({}_{2}\) Concentration on the Variations in Carbon Assimilation and Fluorescence Emission  
For the CO\({}_{2}\) curves with constant irradiance, the proxies of photosynthetic capacity including \(A_{\text{G}}\) and \(\Phi_{\text{PSII}}\) for soybean (Figure 3a,e) and maize (Figure 3c,g) increased with increasing CO\({}_{2}\), until plateaus occurred at a CO\({}_{2}\) concentration of about 500 ppm. However, \(g_{\text{sw}}\) curves declined continuously to nearly 0 in response to the increased CO\({}_{2}\) concentration (Figure 3b,d). Except for abrupt increases at the lowest CO\({}_{2}\) concentrations (<50 ppm) of maize, TchlF\({}_{760}\) and F\({}_{\text{s}}\) for both species responded similarly: they continuously increased until the external concentration was around 500 ppm CO\({}_{2}\) (Figure 3j-l). With the increases in both \(A_{\text{G}}\) and TchlF\({}_{760}\) (F\({}_{\text{s}}\)), steep decreases in NPQ were observed, as expected, but no adjustments in leaf-level energy partitioning were found when the CO\({}_{2}\) concentration exceeded 500 ppm (Figure 3f,h). Excluding measurements at low CO\({}_{2}\) concentrations (<50 ppm), TchlF\({}_{760}\) of soybean and maize was highly correlated with \(A_{\text{G}}\), with \(R^{2}\) = 0.96 and \(R^{2}\) = 0.87, respectively (Table 2); F\({}_{\text{s}}\) also explained 94% and 95% of the variability in the \(A_{\text{G}}\) measurements for soybean and maize, respectively (Table 2). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Species**} & \multirow{2}{*}{**Treatments**} & \multirow{2}{*}{**Fluorescence**} & \multicolumn{4}{c}{\(A_{\text{G}}\)} \\ \cline{4-7}  & & & **Leaf 1** & **Leaf 2** & **Leaf 3** & **Set** \\ \hline \multirow{4}{*}{Soybean} & CO\({}_{2}\) & TChFl\({}_{760}\) & 0.93 & 0.94 & 0.95 & 0.96 \\  & CO\({}_{2}\) & F\({}_{\text{s}}\) & 0.93 & 0.94 & 0.91 & 0.94 \\  & Leaf & TChFl\({}_{760}\) & 0.86 & 0.91 & 0.95 & 0.96 \\  & temperature & F\({}_{\text{s}}\) & 0.81 & 0.92 & 0.75 & 0.89 \\  & & TChFl\({}_{760}\) & 0.99 & 0.95 & 0.99 & 0.99 \\  & ABA & F\({}_{\text{s}}\) & 0.86 & 0.76 & 0.73 & 0.93 \\  & CO\({}_{2}\) & TChFl\({}_{760}\) & 0.83 & 0.83 & 0.92 & 0.87 \\ \multirow{2}{*}{ Maize} & CO\({}_{2}\) & F\({}_{\text{s}}\) & 0.90 & 0.92 & 0.94 & 0.95 \\  & Temperature & TChFl\({}_{760}\) & 0.79 & 0.93 & 0.94 & 0.92 \\  & & F\({}_{\text{s}}\) & 0.48 & 0.85 & 0.78 & 0.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Coefficients of determination (\(R^{2}\)) for the linear regressions between fluorescence radiance and photosynthetic capacity for the measurements driven by CO\({}_{2}\) concentration (ppm), leaf temperature (°C), and abscisic acid (ABA) treatments under constant irradiance of 800 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\). \(A_{\text{G}}\) represents gross carbon assimilation (\(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\)). TChFl\({}_{760}\) and F\({}_{\text{s}}\) represent the total emitted fluorescence radiance at 760 nm (mW m\({}^{-2}\) nm\({}^{-1}\) sr\({}^{-1}\)) and light-adapted steady-state PAM fluorescence. Bold values indicate regression insignificance (\(p\geq 0.05\)). This table analyzes four groups of datasets: three individual samples (leaf numbers 1-3) and their average (Set). n\({}_{\text{CO2}}=8\) for individual leaves and 24 for a set. n\({}_{T}=5\) for individual leaves and 15 for a set. n\({}_{\text{ABA}}=30\) for individual leaves and 90 for a set.