## 3 Results
### WUE\({}_{\rm s}\) at Different Canopy Heights of Larch Forest
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Factors** & **Ta** & **RH** & **VPD** & **PAR** \\ \hline Upper Canopy WUE\({}_{\text{s}}\) & 0.683 \({}^{\star}\) & \(-\)0.832 \({}^{\star\star}\) & 0.831 \({}^{\star\star}\) & 0.963 \({}^{\star\star}\) \\ Middle Canopy WUE\({}_{\text{s}}\) & 0.827 \({}^{\star}\) & \(-\)0.741 \({}^{\star\star}\) & 0.827 \({}^{\star\star}\) & 0.853 \({}^{\star\star}\) \\ Lower Canopy WUE\({}_{\text{s}}\) & 0.643 \({}^{\star}\) & \(-\)0.740 \({}^{\star\star}\) & 0.750 \({}^{\star\star}\) & 0.753 \({}^{\star}\) \\ \hline \hline \end{tabular} \({}^{\star}\) Indicates significance at the 0.05 level. \({}^{\star\star}\) Indicates significance at the 0.01 level. \(n=9\). Ta is air temperature, RH is relative humidity, VPD is vapor pressure deficit, PAR is photosynthetically active radiation.  
\end{table} 
Table 3: Pearson correlation coefficient (r) of WUE\({}_{\text{s}}\) and meteorological factor at different canopy heights of the larch forest. correlated with Gs (\(p\) < 0.01) and the middle and lower WUE\({}_{\rm s}\) were significantly positively correlated with C\({}_{\rm i}\)/C\({}_{\rm a}\) (\(p\) < 0.05), while the upper WUE\({}_{\rm s}\) were not significantly correlated with C\({}_{\rm i}\)/C\({}_{\rm a}\). It can be seen that the trend of WUE\({}_{\rm s}\) in different canopy layers is influenced by photosynthetic parameters, especially Pn and Gs, while C\({}_{\rm i}\)/C\({}_{\rm a}\) has relatively less influence on WUE\({}_{\rm s}\). Effect of Leaf Anatomical Characteristics on WUE\({}_{\rm s}\) at Different Canopy Heights of Larch Forest  
Table 5 shows that the effect of LMA, LT, upper and lower SL and SW and upper and lower GCA of larch-forest leaves at different canopy heights on WUE\({}_{\rm s}\) was upper canopy > middle canopy > lower canopy, and the ranking of the upper and lower ET and upper and lower SD was upper canopy < middle canopy < lower canopy. LMA ranged from 12.44 \(\pm\) 1.01 to 30.84 \(\pm\) 2.05 g/cm\({}^{-1}\) and was significantly greater in the upper canopy than in the middle and lower canopy (\(p\) < 0.01) but with no significant difference between the middle and lower canopy (\(p\) > 0.05). SD ranged from 175 \(\pm\) 9 mm\({}^{-2}\) to 235 \(\pm\) 11 mm\({}^{-2}\) with significant differences between the lower canopy and the upper or middle canopy (\(p\) < 0.01) but no significant differences between the upper and middle levels (\(p\) > 0.05). The upper and lower GCA were significantly different (\(p\) < 0.05), while LT, upper and lower ET and upper and lower SL and SW were not significantly different (\(p\) > 0.05). The leaf-specific LMA and WUE\({}_{\rm s}\) of different canopy heights showed the same trend, with the upper canopy significantly larger than the middle and lower canopy, while the SD and WUE\({}_{\rm s}\) showed opposite trends, with the lower canopy significantly larger than the middle and upper canopy. \begin{table}
\begin{tabular}{c c c c c} \hline
**Factors** & **Pn** & **Tr** & **Gs** & **C\({}_{\rm i}\)/C\({}_{\rm a}\)** \\ \hline Upper Canopy WUE\({}_{\rm s}\) & 0.837 ** & 0.825 * & 0.819 ** & 0.465 \\ Middle Canopy WUE\({}_{\rm s}\) & 0.933 ** & 0.731 * & 0.745 ** & 0.857 * \\ Lower Canopy WUE\({}_{\rm s}\) & 0.926 ** & 0.467 & 0.751 ** & 0.544 * \\ \hline \end{tabular}  
* Indicates significance at the 0.05 level. ** Indicates significance at the 0.01 level. \(n\) = 9. Pn is net photosynthetic rate, Tr is transpiration rate, Gs is stomatal conductivity and C\({}_{\rm i}\)/C\({}_{\rm a}\) is intercellular and atmospheric CO\({}_{2}\) concentration ratio.  
\end{table} 
Table 4: Pearson correlation coefficient (r) of WUE\({}_{\rm s}\) and photosynthetic parameters at different heights canopy of the larch forest.