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

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 [Beta vulgaris ssp, cicla (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 CI (0.01, 40, 80, and 120 mM) in the nutrient solution with Fourfold replication. Solution Na concentrations and ionic strengths were equalized in all treatments by compensating with NaNO3, Increasing CI concentrations in solution did not affect dry weights of either roots or shoots, Activity of Cd2+ in solution was well buffered during plant growth using the resin system. Complexation of Cd2+ by Cl increased soluble Cd in culture solutions but the calculated activity of Cd2+ was not significantly affected by increasing concentrations of Cl in solution, As solution CI concentration increased, Cd concentrations in plant shoots increased from 6.5 to 17.3 mg kg(-1) and in roots from 47 to 106 mg kg(-1). We concluded that enhancement of Cd uptake by CI in soils need not be related only to enhanced diffusion of Cd2+ through soil to the root but that (i) CdCln2-n (in addition to Cd2+) species in solution are phytoavailable and/or (ii) Cl enhances diffusion of Cd2+ through the unstirred liquid layer adjacent to the root surface or through the apoplast to sites of Cd uptake within the root itself.