Uptake and translocation of heavy metals in Raphanus sativus: a comparison of two growing systems

In this study we compare the heavy metals effect on radish plants grown in soil and in hydroponic culture to check whether the plant response to heavy metals (Cd, Cu, Ni and Zn) is affected by the cultural system. In hydroponics all nutrient elements are fully available to the plant, while in soil only a fraction of the total nutrients are available. In order to obtain comparable nutrient availability in both cultural systems, we prepared artificial soils where the available fraction of each element was the same as in the hydroponic nutrient solution. In both growing substrates the heavy metals were given together. The following parameters were monitored: 1) germination percentage 2) biomass production 3) heavy metals quantity in the shoot. In both growth substrates, soil and hydroponic culture, the seed germination percentage (> 90%) was not affected by heavy metals. With no heavy metals added, biomass production of plants grown in soil or in hydroponics was not statistically different. In hydroponics, the addition of heavy metals resulted in a reduction of radish growth while in soil, the differences between the biomass of the controls and the respective treatments was in no case statistically significant. At the same available concentration of heavy metals in both substrates, radish plants grown in hydroponics absorb higher concentrations of heavy metals in comparison with plants grown in soil. These results suggest that when studying the absorption and translocation of metals in vegetables, it is not possible to compare the concentration of heavy metals in a hydroponic solution with the heavy metals concentrations chemically extracted from a soil.