Water contamination by trace metals is one of the main types of pollution in aquatic ecosystems. Aquatic plants can take up heavy metals from the environment. Their capability to absorb the elements differs both among species and their organs. Therefore, it is useful to identify various species and their organs which accumulate the greatest amounts of trace metals.
The stress responses and metal bioaccumulation in combined treatments of copper, zinc, lead and cadmium by the emergent wetland plants Zizania latifolia and Acorus calamus were studied in pot experiments. Growth parameters, physiological indices and metal uptake by the two species were investigated. Results indicated that neither Z. latifolia nor A. calamus could survive in the highest concentrations employed. Compared to controls, plant height, number of roots and biomass of A. calamus significantly decreased in low and medium metal concentration treatments. No significant differences in plant height, number of roots and biomass of Z. latifolia could be demonstrated between the control and low and medium metal treatments. These growth differences between the two species might reflect that the innate metal resistance of Z. latifolia is higher than that of A. calamus. With increasing heavy metal concentrations, the chlorophyll content of both species decreased significantly, and the chlorophyll a/b rate decreased slightly in Z. latifolia and decreased significantly in A. calamus. SOD and POD activity increased in the low metal treatments and decreased in the mid-concentration treatment. Proline content and relative electrolyte leakage rate of the two species increased significantly. Copper, Zn, Pb and Cd concentrations in both species increased with increase of metals in soils, the rank order was Zn>Cu>Pb>Cd in Z. latifolia and Cu>Zn>Pb>Cd in A. calamus. The bio-concentration factor (BCF) for Cd in shoots (leaves and stems) and roots (rhizomes and roots) of the two species were both > 1, whereas the BCFs of Pb in shoots and roots were < 1. In both cases, concentrations of Cu, Zn, Pb and Cd in roots were higher than in shoots suggesting that these two species are basically excluder plants, translocating little metal from roots-shoot. There was a substantial retention function for roots of the two species to heavy metals, and their average retention rates were all greater than 50%. Overall uptake of Cu, Zn, Pb, and Cd by Z. latifolia was greater than by A. calamus in all treatments. Zizania latifolia could be suitable for phytopurification and phytoremediation of wastewater with low-medium concentrations of Cu, Zn, Pb and Cd.