Effect of shading on the accumulation of Cd, Pb and Zn of Sedum plumbizincicola

This study aimed to investigate the effect of shading on the accumulation characteristics of Cd, Pb, and Zn in Sedum plumbizincicola. S. plumbizincicola has strong tolerance and uptake ability for Zn and Cd, and is a promising remediation plant for Zn- and Cd-contaminated soil. To promote the application of S. plumbizincicola in remediation practices of heavy metal polluted soil of Pb-Zn mining area in Yunnan Province, S. plumbizincicola was planted in the slag field of the Lanping Pb-Zn mining area in Nujiang, Yunnan Province. In the experiment, a shade net was laid to reduce the light intensity by 25%, and the effects of shading on plant biomass and chlorophyll; contents and accumulation of Cd, Pb, and Zn in different organs; as well as subcellular distrubition of Cd, Pb and Zn in leaves and stems were investigated. The results indicated that the shading treatment significantly reduced the Cd, Pb, and Zn contents in the stems and leaves of S. plumbizincicola (P<0.01); and significantly decreased the accumulation of Cd, Pb, and Zn in the stems and leaves by 17.6%−67.4% (P<0.05 or P<0.01). Moreover, compared with the no-shading condition, the Cd and Zn enrichment and transfer coefficients of S. plumbizincicola were significantly reduced when grown under shading conditions (P<0.05). The shading treatment significantly decreased the transport coefficient and biological transfer factor of Pb (P<0.05). Under the shading treatment, the Cd content in the leaf cell wall of S. plumbizincicola was significantly reduced (P<0.05), while the Pb content significantly increased (P<0.05). At the same time, the content of Zn in the organelles and soluble parts of S. plumbizincicola was significantly reduced by 11.8%−57.3% (P<0.05). In the stems and leaves of S. plumbizincicola, the HAc-extractable and HCl-extractable forms of Zn, and NaCl-extractable forms of Cd and Pb were dominant. In addition, the shading treatment increased the content of HAc-extractable Cd in the leaves of S. plumbizincicola by three times (P<0.01) and produced a significant reduction in the content of the water-extractable Cd (P<0.05, P<0.01). In addition, the ethanol-, HAc-, and HCl-extractable Zn forms were reduced by 30.2%−58.6% in the leaves of S. plumbizincicola (P<0.01). Thus, shading reduced vacuolar compartmentalization and cell wall retention in S. plumbizincicola as well as the content of insoluble phosphate-like inert heavy metals, and ultimately reduced the ability of S. plumbizincicola to enrich and transport Cd and Zn.