草酸和柠檬酸提高长白落叶松对Pb胁迫的适应性

通过外源添加不同浓度草酸或柠檬酸溶液，系统研究了不同处理时间下，草酸和柠檬酸对土壤Pb胁迫下长白落叶松幼苗多种生理生化特性、元素吸收及生长的影响，特别是叶绿素荧光参数、根系形态特征及养分元素吸收状况。结果表明，Pb胁迫对长白落叶松产生毒害，叶片细胞膜透性和F₀提高，叶片可溶性蛋白含量、叶绿素荧光参数(F_m、F_v、F_v/F_m和F_v/F₀比率)、根系表面积、长度、体积和比根长均下降。细根和叶片K、Ca、Fe、Pb含量及细根Mg含量显著增加，但叶片Mg含量降低，根、茎和叶干质量也显著降低。时间越长Pb对苗木的毒害越重。外源草酸和柠檬酸处理使上述生理生化特性和根系形态指标均向相反方向变化，并显著提高根、茎和叶等各部分干质量，提高了苗木对Pb胁迫的抵抗力和适应性。有机酸对上述指标的影响一般在20或30 d，5.0或10.0 mmol/L效果最佳，且柠檬酸效果强于草酸。草酸和柠檬酸降低苗木细根和叶片Mg、K、Ca含量, 但增加Fe含量。较低浓度有机酸处理时，苗木细根和叶片Pb含量降低，此时苗木对Pb胁迫的解毒机制主要体现在外部排斥机制，而较高浓度时(5.0~10.0 mmol/L)Pb含量却升高，此时内部耐受机制发挥的作用更大，但也不排除2种机制同时起作用的可能性。研究能为有机酸应用于植物修复土壤Pb胁迫提供理论指导，也能为东北林区Pb胁迫土壤的有效利用开辟新思路。 

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 (Fm, Fv, Fv/Fm and Fv/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.