Preliminary studies on the growth, tolerance and phytoremediation ability of sugarbeet (Beta vulgaris L.) grown on heavy metal contaminated soil

Sugarbeet (Beta vulgaris L.) was tested in a greenhouse pot experiment to evaluate its growth, tolerance ability and remediation potential to soils contaminated with cadmium (Cd) and nickel (Ni). Sugarbeet seeds were pre-germinated and four weeks after sowing the seedlings were transplanted to 36 pots. They were left to grow for 12 weeks and then aqueous solutions of nitrate salts of Cd and Ni were added to the soil. The applied treatments were: only Cd(NO3)2.4H2O addition in quantities (g) of Cd0:0, Cd0.5:0.5, Cd5:5, and Cd10:10; only Ni(NO3)2.4H2O addition in quantities (g) of Ni0:0, Ni1:1, Ni10:10, and Ni20:20; a combination of both salts in quantities (g) of Cd0 + Ni0: 0 + 0, Cd0.25 + Ni0.5: 0.25 + 0.5, Cd2.5 + Ni5: 2.5 + 5, Cd5 + Ni10: 5 + 10. At the end of the experiment, the determined DTPA-extractable metal concentrations in soil were up to 225.8 mg Cd kg−1 and 75.4 mg Ni kg−1. Under the Cd treatment, plant growth remained unaffected, with the exception of the leaves' number, which differed significantly among control (Cd0) and highly (Cd10) treated plants on the last measurement date. Nickel affected sugarbeets growth and Ni20 was lethal to the plants. Under the combined Cd and Ni treatment, the toxicity symptoms were milder than in Ni treatment and only the Cd5 + Ni10 treated plants were affected. The higher accumulation rate of Cd and Ni was recorded in the above-ground biomass, with beets also experiencing cadmium and nickel accumulation. Under Cd10 treatment, metal content reached 92.1 mg kg−1 in the aboveground biomass and 14.3 mg kg−1 in beets, while Ni concentrations under Ni10 treatment were up to 283.3 mg kg−1 and 45.9 mg kg−1 respectively. Under the combined Cd and Ni treatments, Cd concentrations were up to 172.5 and 76.7 mg kg−1 in shoots and beets, respectively, while Ni was up to 467.8 and 289.7 mg kg−1, respectively. Metal accumulation (mg per pot) in the single experiments followed the pattern Cd > Ni, mostly due to the higher biomass production in the Cd pots and the higher Cd mobilized content in the soil. In the combined Cd and Ni contamination, Ni accumulation was higher than the Cd accumulation, reflecting a preference by sugarbeet to absorb an ion with lower radius and higher electronegativity. Higher modified translocation factors (mTFs) were obtained for Ni, in the single experiments. In the combined experiment, the mTFs was reduced for both metals due to the combined accumulation of Ni and Cd. Sugarbeet can be considered an interesting candidate for Cd phytoextraction, favored by the biomass produced and accumulation observed but further studies should be conducted in order to evaluate the effect of the soil contamination on the bioethanol yield and quality.