Oxalic and citric acids enhancing adaptation of Changbai Larix olgensis to soil Pb stress

By applying different concentrations of exogenous oxalic acid or citric acid solutions, the effects of organic acids on some physiological and biochemical parameters, element absorption and growth of Pb-stressed Larix olgensis seedlings for different treatment times were studied, especially the effects on chlorophyll fluorescence, root morphology and nutrient absorption. The results showed that, Pb treatment had stressful effects on the seedlings, lipid peroxidation and F₀ in leaves significantly increased, soluble protein contents, chlorophyll fluorescence (F_m, F_v, F_v/F_m and F_v/F₀) in leaves, root surfarea, length, volume and specific root length all decreased. K, Ca, Fe and Pb contents in fine roots and leaves, and Mg contents in fine roots obviously increased, but Mg contents in leaves decreased, and biomass of root, stem and leaf all significantly decreased. The harmful effects were promoted with increasing Pb treatment times. When Pb-stressed plants were exposed to oxalic acid or citric acid, the physiological and root morphological parameters were reversed, and biomass of root, stem and leaf all significantly increased, so exogenous organic acids can improve the tolerance of L. olgensis seedlings to Pb stress. As to the effects of organic acids on the characteristics shown above, the desirable treatment of organic acid was 5.0 or 10.0 mmol/L for 20 or 30 days, and citric acid was more effective than oxalic acid. Oxalic acid or citric acid decreased the contents of Mg, K, Ca in fine roots and leaves, however, Fe contents in fine roots and leaves significantly increased. Under lower concentrations of organic acid treatments, Pb contents in L. olgensis fine roots and leaves decreased, at this time the detoxification mechanism of the seedlings to Pb stress was mainly the external rejection mechanism, however, Pb contents increased under higher concentrations (5.0-10.0 mmol/L), here internal resistance mechanism was dominant, and it's also possible that two mechanisms work together. The study can theoretically guide phytoremediation of Pb-stressed soils with organic acid and L. olgensis seedling amendments, and as well as open up new ideas to the effective utilization of the Pb-stressed soil in northeastern China.