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 (D-4) and 5.82 m (D-5) were lower and a little higher than that at 3.82 m (D-3), respectively. Compared with C-i and L-s of the D-3 trees, C-i decreased and L-s increased at 4.74 m, however, C-i increased and L-s decreased at D-5. 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. PN of the D-3 trees was significantly higher than those at D-4 or D-5. The trees of D-4 and D-5 did not show a significant difference in their PN, indicating that there are mechanisms of P. euphratica tolerance to mild and moderate drought stress.