Study on Physiological Response and Tolerance of Populus yunnanensis Seedlings to Cadmium and Zinc Stress

To investigate the growth and physiological responses of Populus yunnanensis, and to clarify its tolerance characteristics under cadmium(Cd), zinc(Zn) and their combined(Cd-Zn) stress, the experiment was carried out by soil culture pot. The results showed as follows: Cd and Zn stress did not significantly change plant height, ground diameter, and total biomass, but Zn stress significantly increased full root length, root surface area and root volume, while Cd-Zn stress significantly decreased full root length. Zn stress improved the nursery stock quality of P. yunnanensis, Cd stress made the growth worse, and Cd-Zn stress was the worst growth status. Photosynthetic pigment content and net photosynthetic rate were not changed by single stress of Cd and Zn. Under Cd-Zn stress, chlorophyll content decreased significantly, while net photosynthetic rate and light response characteristic parameters did not change significantly. Dark respiration rate(R_d) and light compensation point(LCP) were significantly increased under Cd stress, and light saturation point(LSP) was significantly increased under Zn stress. Cd and Cd-Zn stress could stimulate the oxidative stress defense system of P. yunnanensis, the activities of superoxide dismutase(SOD) and catalase(CAT) were significantly increased, while the contents of malondialdehyde(MDA) and total phenol(TPh) were not significantly changed, and SOD, CAT, MDA and TPh were not significantly changed under Zn stress. The seedlings of P. yunnanensis showed tolerance to single and combined stress of Cd and Zn, and could be used as an important candidate tree for ecological remediation of Cd and Zn polluted soil. The total tolerance values(D) of all treatments followed the sequence of Zn>CK>Cd> Cd-Zn.