Assessment of cadmium uptake and nutrient content in sunflower plants grown under Cd stress

Sunflower plants were grown on soil contaminated with several levels of Cd (from 0.3 to 15 mg Cd kg/soil). Cd and nutrient (Cu, Zn, Fe, Ca, K, Mg) contents were evaluated in root and aboveground biomass during the vegetative growth period (from the emergence of the cotyledon leaves to the flower bud phase). An overall increase of Cd content was found in the plants during the growing cycle. Significant interactions were found between Cd contamination levels and phenological stages for Cu, Fe, Ca and Mg content in the whole plant. Cd levels involved significant increases of such nutrients only at the flower bud phase. At this stage, significant interactions between Cd levels in soil and plant portions (root and shoot) were found only for micronutrients (Zn, Cu, Fe). The translocation of micronutrients from root to the shoot was negatively affected by Cd, which probably interferes with the mechanisms of the element transport in the plant. Root stored about 70% of the total Cd and showed greater imbalance in nutrient content compared to the aboveground portion. Cadmium affects plant nutritive status in a different way depending on Cd contamination level, nutrient considered, plant portion and phenological stage.