油葵和苦荬菜根际土壤中镉和锌的活化机制及修复潜力比较

Comparison of Helianthus annuus L.and Ixeris polycephala Cass for Cd and Zn Activation Mechanisms in Rhizosphere Soil and Remediation Potential

【目的】研究油葵和苦荬菜根际土壤固、液相对镉(Cd)和锌(Zn)的活化机制,比较两种植物在轻、中度复合污染农田的修复潜力。【方法】通过大田试验种油葵和苦荬菜,测定成熟期土壤的pH值、有机酸、重金属总量及其生物有效性;测定土壤溶液中的溶解性有机质(DOM)、主要离子、水溶态重金属及其形态分布;测定植物各部位中重金属的浓度及形态,通过计算重金属在植物中的富集系数(BCF)和转运系数(TF),比较两种植物对土壤重金属污染的修复潜力。【结果】油葵和苦荬菜根系分泌的低分子有机酸均使根际土壤pH值下降明显,显著低于非根际土壤(P<0.05);苦荬菜根际土中低分子有机酸及DOM的浓度显著高于油葵根际土(P<0.05)。两种植物根际土壤溶液中的Cd以离子态和DOM结合态为主,Zn以离子态为主;两种植物根际土壤中有效态的Cd差异不显著,油葵根际有效态Zn显著高于苦荬菜;两种植物根际土壤的Zn和Cd有效态与土壤溶液中Cd-DOM和Zn-DOM呈显著相关。苦荬菜根对重金属的富集能力较强,但油葵地上部分能吸收转运更多的Cd和Zn,并在叶中以毒性较低的不溶性磷酸盐结合态和草酸结合态富集。【结论】两种植物根际分泌的有机酸可以增加根际土壤中的Cd-DOM和Zn-DOM的浓度,提高土壤中的Cd和Zn的有效性,苦荬菜根际对重金属有较强的活化能力,但油葵地上部分对Cd和Zn的吸收转运能力更强。两种植物都具有较强的土壤重金属修复潜力,但从经济角度出发,油葵更适合现阶段我国农田重金属污染的修复。

[objective]The mobilization mechanisms of cadmium(Cd)and zinc(Zn)by solid and liquid phase of rhizosphere soil of Helianthus annuus L.(sunflower)and Ixeris polycephala Cass were investigated to compare the remediation potential of the two plants in light and moderate Cd-Zn contaminated farmland soil.[Method]Sunflower and Ixeris polycephala Cass were planted in field trials.The pH value,organic acid concentration,total concentration and bioavailable concentration of heavy metals in soil from maturity period were determined.The concentration of dissolved organic matter(DOM),ions,water-soluble heavy metals and its morphological distribution were calculated.The concentrations and chemical forms of heavy metals in different parts of plants were determined.The bioconcentration factors(BCF)and transport factors(TF)of heavy metals in plants were calculated to compare the remediation potential between two plants for heavy metal pollution soil.[Result]The pH value of rhizosphere soil was decreased significantly by low molecular organic acids secreted from the root of sunflower and Ixeris Polycephala Cass,which was significantly lower than those in non-rhizosphere(P<0.05).The concentration of low molecular organic acids and DOM in the rhizosphere soil of Ixeris polycephala Cass were significantly higher than those in the rhizosphere soil of sunflower(P<0.05).The Cd in the rhizosphere soil solution of the two plants was mainly in the ionic state and DOM-bound state,and the Zn was mainly in the ion state.No significant difference wwa observed for the concentration of bioavailable Cd in rhizosphere soil between the two plants,the bioavailable Zn in the rhizosphere of sunflower was significantly higher than that of Ixeris Polycephala Cass.The concentrations of bioavailable Zn and Cd in rhizosphere soil between two plants were correlated with Cd-DOM and Zn-DOM in soil solution.The root of Ixeris polycephala Cass showed an outstanding accumulation heavy metal ability,but sunflower could absorb and transport more Cd and Zn from root to shoot,and the heavy metals were accumulated with undissolved phosphate and oxalate form in leaves of sunflower.[Conclusion]The organic acids secreted by rhizosphere of two plants could increase the concentration of Cd-DOM and Zn-DOM in rhizosphere soil and improve the availability of Cd and Zn in soil.The root of Ixeris polycephala Cass presented remarkable mobilize ability to Cd and Zn,but the shoot of sunflower had outstanding absorption and transport ability for Cd and Zn.Both sunflower and Ixeris polycephala Cass were have remediation potential for heavy metal in soil,but sunflower was more suitable for remediation of heavy metal contaminated farmland in China from the economic point of view.