磷对铅、锌和镉在土壤固相-液相-植物系统中迁移转化的影响

Effects of Phosphorus Application on Translocation of Lead,Zinc and Cadmium in the Soil-Plant System

在盆栽条件下,以磷酸二氢钾作为磷（P）添加剂,以空心菜为指示植物,借助模型Visual MINTEQ研究了P对污染土壤中铅（Pb）、锌（Zn）和镉（Cd）在土壤固相-液相之间以及土壤-根系-地上部的迁移累积的影响.实验设了6个P剂量水平：0（CK）、0.18（P0.18）、0.36（P0.36）、0.72（P0.72）、1.08（P1.08）、1.44（P1.44）,P剂量水平是按照P/Pb物质量的比例（mol/mol）为基础而设计的.结果表明,与对照相比,添加P处理污染土壤后,显著（p〈0.05）降低了空心菜地上部吸收的重金属Pb、Zn和Cd的含量,降低幅度分别为53%-92%、35%-71%和59%-86%,降低了根系吸收累积重金属Pb的含量,增加了根系吸收的Zn的含量,但对Cd吸收量无显著影响.增加P的剂量水平,根系向地上部转运的Pb、Zn和Cd的量的呈指数级下降趋势.地上部吸收的各元素的相关分析结果表明,元素Pb与元素Zn、Cd是显著正相关关系,其中相关系数最高的是Pb与Zn（r=0.993,p〈0.01）,其次是Pb与Cd（r=0.986,p〈0.01）.说明Pb与Zn、Cd在空心菜从根系到地上部分转运的过程中是协作关系.添加P后,提高了土壤pH,从而降低了土壤水溶性Cd的含量,Zn变化不显著,增加了土壤水溶性总Pb含量.平衡液中Pb的主要存在形态是PbHPO4、PbOH＋、PbH2PO4＋等3种络合形态.结果还表明,根系吸收Pb的量与土壤水溶性Pb含量具有显著的负相关关系,相关系数-0.872（p〈0.05）.P处理降低了土壤水溶性Zn、Cd的含量,却促进了根系吸收,这是Zn、Cd与Pb的不同之处.P具有显著降低复合污染土壤中Pb、Zn和Cd植物毒性的作用.

A pot experiment was conducted to determine the influence of phosphorus （P） application on the translocation and accumulation of lead （Pb）, zinc （Zn）, and cadmium （Cd） in a soil solid-liquid-plant system using a plant Swamp Morningglory （Ipornoea aquatica Forsk） as an indicator and Visual MINTEQ model. A contaminated soil containing 22 830 mg·kg^-1 Pb, 746 mg·kg^-1 Zn, and 10 mg·kg^-1 Cd was amended with P as KH2 PO4 at 0 ： 1,0.18 ： 1, 0. 36 ： 1,0.72 ： 1,1.08 ： 1, and 1.44 ： 1 P： Pb mole ratios. The results showed that Pb concentration in the root was significantly decreased after P application, while the Zn concentration were increased, but no impact on Cd concentration after P application, compared to the control. Further more, concentrations of Pb, Zn, and Cd in plant tissue were sharply reduced after P application by 53%-92%, 35%-71%, and 59%-86%, respectively; Concentrations decreased exponentially with increasing amount of P; Relationship between Pb and Zn （ r = 0.993 ,p 〈 0.01） ,between Pb and Cd （ r = 0.986,p 〈 0.01） suggested that there was a positive relationship between the mechanisms controlling the phytoavailability of Pb, Zn, and Cd. It was suggested that Cd concentrations in the soil solution were reduced generally by P application as a result of the increased soil pH, and Zn concentrations were no changed, but Pb concentrations were increased. Species distribution showed that PbHPO4, PbOH ＋ and PbH2 PO4 were the main complexation species of Pb in the soil equilibrium solution after P application. It was also suggested that Pb accumulation by root were negatively correlated to Pb in soll solution with coefficient of - 0.872（p 〈 0.05）, and that water soluble Zn and Cd concentrations were reduced while the concentrations in root tissues were increased after P addition. These results indicate the difference between Zn, Cd and Pb and suggest that P as KH2PO4 successfully decreased the phytotoxicity of Pb, Zn, and Cd in the contaminated soil.