Accumulation of cadmium, zinc and copper by Helianthus annuus L.: impact on plant grawth and uptake of nutritional elements

We investigated the effects on physiological response, trace elements and nutrients accumulation of sunflower plants grown in soil contaminated with: 5 mg kg−1 of Cd; 5 and 300 mg kg−1 of Cd and Zn, respectively; 5, 300, and 400 mg kg−1 of Cd, Zn, and Cu, respectively. Contaminants applied did not produce large effects on growth, except in Cd-Zn-Cu treatment in which leaf area and total dry matter were reduced, by 15%. The contamination with Cd alone did not affect neither growth nor physiological parameters, despite considerable amounts of Cd accumulated in roots and older leaves, with a high bioconcentration factor from soil to plant. By adding Zn and then Cu to Cd in soil, significant were the toxic effects on chlorophyll content and water relations due to greater accumulation of trace elements in tissues, with imbalances in nutrients uptake. Highly significant was the interaction between shoot elements concentration (Cd, Zn, Cu, Fe, Mg, K, Ca) and treatments. Heavy metals concentrations in roots always exceeded those in stem and leaves, with a lower translocation from roots to shoots, suggesting a strategy of sunflower to compartmentalise the potentially toxic elements in physiologically less active parts in order to preserve younger tissues.