EFFECTS OF SULFATE ON CADMIUM UPTAKE BY SWISS-CHARD - I - EFFECTS OF COMPLEXATION AND CALCIUM COMPETITION IN NUTRIENT SOLUTIONS

The impacts of both sulfate (SO4) and calcium (Ca) concentrations in s olution on plant uptake of cadmium (Cd) vary according to effects on b oth sorption of Cd by soil and on uptake by the plant root. This study investigated how complexation of Cd by SO4 affected plant Cd uptake i n nutrient solution. Swiss chard (Beta vulgaris L. cv. Fordhook Giant) was grown in nutrient solution with SO4 concentrations varying betwee n 8 mM and 58 m M, with ionic strength maintained constant across trea tments using nitrate (NO3). In a separate experiment, solution Ca conc entrations was also varied to compensate for SO4 complexation by Ca. P lant growth was unaffected by increasing SO4 concentrations in solutio n. Despite considerable reductions in free Cd2+ ion activities in solu tion by increasing SO4 concentrations, plant Cd concentrations were un affected. Similarly, plant Cd concentrations were unaffected by increa sing Ca concentrations in solution to compensate for SO4 complexation of Ca. These data suggest that the CdSO40 complex is taken up by plant s with equal efficiency to the free Cd2+ ion.