Influence of organic matter on the uptake of cadmium, zinc, copper and iron by sorghum plants

This article describes an experiment, carried out under controlled environment conditions, to investigate the effects of a fulvic acid fraction of soil organic matter on growth, cadmium (Cd) uptake and redistribution by sorghum. In addition the uptake of copper (Cu), zinc (Zn) and iron (Fe) was also determined. Sorghum was grown in nutrient solutions with 0, 0.1, 1 and 10 mg Cd dm−3, in the absence and presence of organic matter (32 mg C dm−3), for various periods up to 20 days. A decrease in sorghum biomass due to Cd toxicity was observed at 10 mg Cd dm−3, but for concentrations of 0.1 and 1 mg Cd dm−3 the biomass was increased compared with control, without visual toxicity symptoms. The presence of organic matter (OM) further increased biomass production. Cadmium was mainly retained in sorghum roots, as usually found in tolerant plants, but Cd accumulation in sorghum was greater than in other Gramineae, or even more tolerant plants such as lettuce. The presence of OM decreased the bioavailability of Cd that was partially retained in solution by the OM ligands. However, OM promoted the translocation of Cd to shoots, an effect that may pose a risk to public health because plant-animal transfer of Cd could be enhanced. The presence of OM decreased the uptake of Cu, Zn and Fe. The presence (vs. absence) of 0.1 mg Cd dm−3 enhanced the uptake of Fe, both in the absence and presence of OM.