Growth Response And Metal Accumulation Of Sedum Alfredii Hance To Complex Supply Levels Of Zn, Cd, And Pb

Phytoremediation of heavy metal polluted environment has become the frontier and hot research area of environmental and biological science. To identify or breed suitable plant materials which can tolerate and accumulate multiple metals, fast growth and wide adaptation is of most importance for phytoremediation. The objectives of this study were to investigate on growth response and metal accumulation of Sedum alfredii Hance to complex levels of Zn, Cd, and Pb in both nutrient solution and soil. The major results were summarized as follows:1. The optimal growth of S. alfredii in term of the maximum dry matter yield was observed at Zn/Cd complex levels of 500/100umol L-1. Plant Cd or Zn concentrations increased with increasing Cd or Zn supply. During 20 d treatment, the highest Cd concentration in the leaves reached 12.1 g kg-1 at Zn /Cd level of 50/400 μmol L-1 and that of Zn in the stems was 23.2 g kg-1 at Zn/Cd level of 1000/50 umol L-1. The distribution of Cd in different plant parts decreased in the order: leaf > stem >> root, whereas that of Zn was: stem > leaf >> root. The accumulation of Cd and Zn in the shoots and roots of S. afredii increased with increasing of Zn /Cd supply levels, peaked at Zn/Cd levels of 250/400 and 500/100 μmol L-1, respectively. The highest Cd and Zn uptake by the shoots was approximate to 5 and 11 mg plant-1, and was over 20 and 10 times higher than those in the roots, respectively. Zinc supply at levels < 500 μmol L-1 increased plant Cd concentrations, whereas high Zn supply decreased root Cd but did not affect leaf Cd concentrations in S. alfredii. Low Cd supply increased Zn concentration in the leaves, but Cd supply higher than 50μmol L-1 considerably reduced root Zn concentrations, especially at low Zn level. These results indicate that S. alfredii can tolerate high Zn/Cd complex levels and has an extraordinary ability to hyperaccumulate not only Zn but also Cd. It could provide a new valuable plant material for understanding the mechanisms responsible for co-hyperaccumulation of Zn and Cd as well as for phytoremediation of the Cd/Zn complex polluted soils.2. Shoot Zn concentration of old-mining ecotype of Sedum alfredii Hance was farhigher than that of the non-mining ecotype grown at the same external Zn concentration in the nutrient solution. The highest Zn concentration in the stem of the old-mining ecotype reached 19.9 g kg-1, however, stem Zn of the non-mining ecotype was 1.3 g.kg-1 at Pb/Zn level of 100/2000 umol L-1. Shoot Pb concentration of old-mining ecotype was also higher than that of the non-mining ecotype with the same Pb supply levels. The maximum Pb concentration in the stem was 0.4 6g kg-1 at Pb/Zn level of 400/500 umol L-1. Zinc distribution was different between the two ecotypes, being leaves>stems>roots for the old-mining ecotype, but roots>stems>leaves for the non-mining ecotype. The highest Zn and Pb uptake by the shoots of in the old-mining ecotype was approximate to 7.9 and 0.144 mg plant-1, respectively, but those in non-mining ecotype was only approximate to 0.23 and 0.056 mg plant-1. The results indicate that the Pb and Zn interaction on the growth and Pb/Zn accumulation by the plant largely depend on Pb/Zn supply, plant part and ecotype. Interactive pattern of Zn with Pb in the old-mining ecotype seemed to be antagonistic, whereas addition of Zn at proper levels could enhance Pb uptake by the root. And high Zn increased Pb concentration in roots and leaves of the non-mining ecotype, but decreased Pb accumulation in the stems , whereas high Pb inhibited Zn absorption by roots and leaves of non-mining ecotype.3. We conducted 2-year field experiments to investigate the relatively long-term effect of soil amendments on the growth and metal accumulation of S. alfredii at a site near a smelting factory. The results from field trials showed that old-mining ecotype of S.alfredii could not only tolerate high soil Zn, Pb, Cu, but also has special ability to absorb and translocate metals to the above-ground parts. Zinc accumulation by the shoot...