Effect of Mn Toxicity on Ecophsiological Responses in Two Populus Cathayana Populations

The cuttings of Populus cathayana was exposed to Hoagland´s solution containing four different manganese (Mn) concentrations (0, 0.1, 0.5 and 1 mM) in a greenhouse to characterize the physiological and biochemical basis of Mn resistance in woody plants. Two contrasting populations of P. cathayana were used in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that high concentration of Mn caused significant decrease in shoot height and biomass accumulation. Moreover, Mn treatments caused the accumulation of hydrogen peroxide (H₂O₂), and then resulted in oxidative stress indicated by the oxidation of proteins. Many ecophysiological responses were employed to cope with the toxicity of Mn including the increase in the contents of non-protein thiol (NP-SH), reduced glutathione (GSH), phytochelatins (PCs) for the chelation of Mn and for the antioxidant of reactive oxygen species. On the other hand, there were different responses to Mn stress between the two contrasting populations. Compared with the dry climate population, the wet climate population not only accumulated more Mn in plant tissues especially in leaves, but also exhibited lower activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), thus caused more serious oxidative damage. Therefore, our results showed that the wet climate population was more susceptible to Mn stress than the dry climate population.