Abstract: In order to explore the growth and photosynthetic physiological responses of Populus yunnanensis under cadmium and lead stress, hydroponics was used to carry out stress experiment on P. yunnanensis seedlings. The results show that under cadmium stress, the plant height of P.yunnanensis had no significant change, while the total root length decreased significantly, and the ground diameter increased significantly at the cadmium concentration of 100 μmol·L^-1. Under Pb stress, the plant height and total root length of P.yunnanensis decreased significantly, while the ground diameter increased significantly at Pb concentrations of 50 and 100 μmol·L^-1. Under Cd and Pb stress, MDA content increased with the increase of stress concentration, and total phenol content increased significantly only at the stress concentration of 100 and 200 μmol·L^-1. The chlorophyll content of 200 μmol·L^-1 Cd treatment, 100 μmol·L^-1 Pb treatment was significantly lower than that of 0 μmol·L^-1 Pb and Cd treatment (control). The maximum photochemical efficiency and potential activity of PS Ⅱ were significantly lower than those of control at 100 μmol·L^-1cadmium concentration. Under cadmium stress, the net photosynthetic rate of P.yunnanensis decreased with the increase of stress concentration, while under lead stress, the net photosynthetic rate first increased and then decreased with the increase of stress concentration. The tolerance of P. yunnanensis to Cd was the strongest when the concentration was 50 μmol·L^-1, and it was the strongest when the concentration was 100 μmol·L^-1 under Pb stress, and the tolerance to Cd was stronger than that to Pb.

Key words: Populus yunnanensis, cadmium stress, lead stress, photosynthetic physiology