Effect of Soil Solution Chloride on Cadmium Availability to Swiss Chard

Abstract

AbstractPotted soil experiments were conducted to analyze how higher Cl concentrations in soil enhance Cd uptake by plants. Two soils (W,L) were moistened with complete nutrient solution containing either NaCl or NaNO3 at concentrations ranging from 0 to 120 mmol L−1. Swiss chard (Beta vulgaris L., cv. Fordhook Giant) was grown in the soils until the 4th leaf appeared (15 d on soil W, 20 d on soil L). Plant dry weights generally decreased with increasing salt concentration, but were not significantly affected by the type of Na salt. For both soils, shoot Cd concentrations in the 120 mmol L−1 NaCl treatment almost doubled those in the zero salt treatments. In contrast, increasing NaNO3 concentrations either reduced shoot Cd concentration (soil L) or had no effect (soil W). Increasing concentrations of NaCl in the soil solution significantly increased the Cd concentration in solution from 65 to 400 nmol L−1 (soil W) and from 64 to 300 nmol L−1 (soil L). Increasing concentrations of NaNO3 in solution had no effect on Cd concentrations in solution. Speciation calculations predicted that the solution concentration of the free metal ion Cd2+ was not significantly affected by the NaCl (both soils) or NaNO3 (soil L) treatments. In soil W, the predicted Cd2+ concentrations in soil solution slightly decreased with increasing NaNO3 rate. It is concluded that the enhancing effect of NaCl on Cd uptake is due to chloride complexation of Cd.