Characterization of photosynthesis of Populus euphratica grown in the arid region

Net photosynthetic rate (P _N), stomatal conductance (g _s), intercellular CO₂ concentration (C _i), transpiration rate (E), water use efficiency (WUE), and stomatal limitation (L_s) of Populus euphratica grown at different groundwater depths in the arid region were measured. g _s of the trees with groundwater depth at 4.74 m (D₄) and 5.82 m (D₅) were lower and a little higher than that at 3.82 m (D₃), respectively. Compared with C _i and L_s of the D₃ trees, C _i decreased and L_s increased at 4.74 m, however, Ci increased and L_s decreased at D₅. Hence photosynthetic reduction of P. euphratica was attributed to either stomatal closure or non-stomatal factors depending on the groundwater depths in the plant locations. P _N of the D₃ trees was significantly higher than those at D₄ or D₅. The trees of D₄ and D₅ did not show a significant difference in their P _N, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.