## 3 Results
### Different Tree Species Resistance Assessment
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sampling** & \multicolumn{2}{c}{**Tree Species**} & \multicolumn{2}{c}{_S. oblata_} & \multicolumn{2}{c}{_P. cersifera_} & \multicolumn{2}{c}{_U. pumila_} \\ \cline{2-7}
**Time** & **Leaf Age** & **10 Days** & **40 Days** & **10 Days** & **40 Days** & **10 Days** & **40 Days** \\ \hline \multirow{7}{*}{1-Sep} & T1 & 0.67 & 0.82 & 0.7 & 0.81 & 0.85 & 0.64 \\  & T2 & 0.5 & 0.63 & 0.5 & 0.85 & 0.59 & 0.75 \\  & T3 & 0.49 & 0.25 & 0.16 & 0 & 0 & 0.25 \\  & Average & 0.55 & 0.57 & 0.45 & 0.56 & 0.48 & 0.55 \\  & Resistance Order & 1 & 1 & 3 & 2 & 2 & 3 \\  & T1 & 0.83 & 0.74 & 0.88 & 0.76 & 0.71 & 0.91 \\  & T2 & 0.62 & 0.81 & 0.65 & 0.82 & 0.69 & 0.77 \\
9-Sep & T3 & 0 & 0.05 & 0 & 0 & 0 & 0 \\  & Average & 0.48 & 0.53 & 0.51 & 0.53 & 0.47 & 0.56 \\  & Resistance Order & 2 & 2 & 1 & 3 & 3 & 1 \\  & T1 & 0.54 & 0.48 & 0.45 & 0.71 & 0.5 & 0.52 \\  & T2 & 0.89 & 0.63 & 0.88 & 0.57 & 0.67 & 0.94 \\
19-Sep & T3 & 0.4 & 0.2 & 0.35 & 0.2 & 0.2 & 0.06 \\  & Average & 0.61 & 0.44 & 0.56 & 0.49 & 0.46 & 0.5 \\  & Resistance Order & 1 & 3 & 2 & 2 & 3 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Function value of subordination and the comprehensive judgment on SO\({}_{2}\) resistance of the three tree species. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Tree Species** & \multicolumn{2}{c}{**Stomatal**} & \multicolumn{2}{c}{**Leaf Tip**} & \multicolumn{2}{c}{**Leaf Middle**} & \multicolumn{2}{c}{**Leaf Base**} \\ \cline{2-5} _S. oblata_ & & & 22.20 \(\pm\) 8.37 c & 29.84 \(\pm\) 9.37 b & 35.18 \(\pm\) 4.95 a \\ _P. censifera_ & SL & 25.12 \(\pm\) 3.38 & 22.90 \(\pm\) 7.72 & 23.89 \(\pm\) 4.28 \\ _U. pumila_ & & 20.46 \(\pm\) 8.71 & 24.45 \(\pm\) 7.68 & 23.28 \(\pm\) 8.02 \\ _S. oblata_ & & 4.13 \(\pm\) 1.40 & 4.00 \(\pm\) 1.28 & 5.80 \(\pm\) 1.59 \\ _P. censifera_ & SW & 5.25 \(\pm\) 1.14 & 5.27 \(\pm\) 1.86 & 5.66 \(\pm\) 2.01 \\ _U. pumila_ & & 2.23 \(\pm\) 1.24 b & 3.34 \(\pm\) 1.39 & 3.63 \(\pm\) 1.26 a \\ _S. oblata_ & & 0.20 \(\pm\) 0.07 a & 0.14 \(\pm\) 0.04 c & 0.16 \(\pm\) 0.03 b \\ _P. censifera_ & SA & 0.21 \(\pm\) 0.04 & 0.24 \(\pm\) 0.08 & 0.23 \(\pm\) 0.06 \\ \hline \hline \end{tabular} \(\overline{\text{SL}}\), stomatal length; SW, stomatal width; SA, stomatal aperture.  
\end{table} 
Table 7: Stomatal aperture characteristics of all three tree species in different leaf zones (9 September). Within each treatment and date, statistical differences between 10 days and 40 days (\(p\) < 0.05) are denoted with lower case letters a, b, and c. Data represent means \(\pm\) SE (\(n\) = 9). _S. oblate_ leaves are usually green, _U. pumila_ leaves tend to be yellow or yellow-green, and _P. cerasifera_ leaves are usually red. The reddening of the leaf color in many tree species is a protective response induced by persistent water and energy imbalance [52]. Tree species with yellowing leaves are accompanied by increased stressors, such as water and higher leaf temperatures, which can be alleviated by high leaf temperatures after rapid chlorophyll breakdown. The process of chlorophyll imbalance is associated with water and energy imbalances, such as drought and high temperatures, in many non-red-leaved tree species. In this study, the overall leaf temperature performance of different tree species after stress was ranked as follows: _P. cerasifera > U. pumila. > S. oblate_. Photosynthetic performance was ranked as follows: _S. oblate > P. cerasifera > U. pumila_. According to these results, along with the change in leaf color, leaf temperature often increased while stomatal conductance decreased, transpiration intensity decreased, and photosynthesis impaired.