ZINC, LEAD AND CADMIUM ACCUMULATION AND TOLERANCE IN TYPHA-LATIFOLIA AS AFFECTED BY IRON PLAQUE ON THE ROOT SURFACE

The effects of iron plaque on the growth of Typha latifolia L. and its accumulation of zinc (Zn), lead (Pb) and cadmium (Cd) were investigat ed under field conditions and in nutrient solution cultures in the lab oratory. In the field, Zn concentrations (but not Cd) on the root surf ace were positively related to Fe concentrations on the root surface. In the laboratory, seedlings with and without iron plaque on their roo ts were exposed to 2.0 and 1.0 mu g ml(-1) Zn for 3 and 72 days and to 10.0 mu g ml(-1) Pb and 0.2 mu g ml(-1) Cd for 48 days. Zn accumulati on was similar in seedlings with and without plaque when exposed to 2. 0 mu g ml(-1) Zn for 3 days. Over the longer growth periods then was n o significant difference in root and shoot dry weights when seedlings with and without plaque were treated with control or metal solutions. Root lengths both in the control and the Cd solution were significantl y shorter in seedlings with plaque than in those without. Zn was absor bed fairly equally on root surfaces with and without plaque; however, roots with plaque absorbed more Pb, but less Cd, than those without. T he presence of plaque did not alter Zn, Pb and Cd translocation in see dlings in the nutrient solutions. Most of the Pb and Cd taken up was r etained in the roots, whereas most of the Zn taken up was retained in the shoots, suggesting that root tissue rather than the root surface o r plaque is the main barrier for Pb and Cd transport. However, plaque may act as an effective Fe reservoir to increase Fe ion concentrations in active cells and then ameliorate metal toxicity. (C) 1998 Elsevier Science B.V.