Chloride increases cadmium uptake in Swiss chard in a resin-buffered nutrient solution

Abstract

<jats:title>Abstract</jats:title><jats:p>One of the possible hypotheses to explain the high Cd availability at elevated Cl concentration in soil is that chloro‐complexes of Cd are available for root uptake. In order to test this hypothesis, Swiss chard [<jats:italic>Beta vulgaris</jats:italic> ssp. <jats:italic>cicla</jats:italic> (L.) Koch, cv. Fordhook Giant) was grown in nutrient solution continuously recirculated over a chelating resin (Chelex‐100) partially loaded with Cd. Treatments were increasing concentrations of Cl (0.01, 40, 80, and 120 m<jats:italic>M</jats:italic>) in the nutrient solution with fourfold replication. Solution Na concentrations and ionic strengths were equalized in all treatments by compensating with NaNO<jats:sub>3</jats:sub>. Increasing Cl concentrations in solution did not affect dry weights of either roots or shoots. Activity of Cd<jats:sup>2+</jats:sup> in solution was well buffered during plant growth using the resin system. Complexation of Cd<jats:sup>2+</jats:sup> by Cl increased soluble Cd in culture solutions but the calculated activity of Cd<jats:sup>2+</jats:sup> was not significantly affected by increasing concentrations of Cl in solution. As solution Cl concentration increased, Cd concentrations in plant shoots increased from 6.5 to 17.3 mg kg<jats:sup>−1</jats:sup> and in roots from 47 to 106 mg kg<jats:sup>−1</jats:sup>. We concluded that enhancement of Cd uptake by Cl in soils need not be related only to enhanced diffusion of Cd<jats:sup>2+</jats:sup> through soil to the root but that (i) CdCl<jats:sup>2‐<jats:italic>n</jats:italic></jats:sup><jats:sub><jats:italic>n</jats:italic></jats:sub> (in addition to Cd<jats:sup>2+</jats:sup>) species in solution are phytoavailable and/or (ii) Cl enhances diffusion of Cd<jats:sup>2+</jats:sup> through the unstirred liquid layer adjacent to the root surface or through the apoplast to sites of Cd uptake within the root itself.</jats:p>