Effects of Zn Exposure on Populus simonii Seedling Growth and Its Resistance to Leaf Rust

Abstract

Heavy metals are serious pollutants that affect the growth and disease resistance of woody plants. Herein, the enrichment characteristics of an essential element (Zn) in Populus simonii seedlings, as well as the effects of Zn stress on seedling growth and resistance to leaf rust, were investigated. Zn contents in roots, stems, and leaves of treatment groups were significantly increased. Zn stress at all concentrations significantly inhibited the biomass of seedlings. Under the low, middle, and high Zn treatments, compared with the control group, CAT activity significantly decreased by 36%, 21%, and 14%; SOD activity significantly decreased by 13%, 8%, and 5%; PPO activity significantly decreased by 27%, 31%, and 47%; TI activity significantly decreased by 48%, 55%, and 61%, and CI activity significantly decreased by 10%, 20%, and 14%, respectively. In the natural environment, we accidentally discovered that P. simonii was infected with leaf rust, and Zn stress significantly increased the rust disease index. The disease index correlated positively with Zn content in leaves and negatively with the chemical defense indexes. Taken together, Zn stress causes a strong growth toxicity in P. simonii seedlings, and the reduced chemical defense under Zn stress increases the susceptibility of seedlings to leaf rust.