Metal Accumulation and Tolerance of Energy Willow to Copper and Nickel under Simulated Drought Conditions

The aim of this study was to determine the effect of drought on the accumulation and tolerance of energy willow (Salix viminalis L. var. ‘Gigantea’) to copper (Cu) and nickel (Ni) in the context of phytoremediation potential of the plant and biomass production under adverse water conditions. Drought was simulated with polyethylene glycol (PEG-6000. 5%), and metals were added at a concentration of 1 mM. Plants were cultivated in greenhouse conditions for 21 days according to the experimental variants: control, Cu, Ni, PEG, PEG + Cu and PEG + Ni. The results indicate high toxicity of Cu (chlorosis, necrosis, decrease in biomass, plant dehydration, increase in the content of proline and phenolic compounds), and PEG + Cu co-treatment increased the toxicity of the metal. Ni applied at the same concentration did not cause toxicity symptoms. The willow exhibits the ability to accumulate Ni, and mutual application of PEG + Ni increased Ni uptake to new shoots. Cu caused elevated accumulation of proline and phenolics in leaves accompanied with a decreased carbon and nitrogen content in roots in favor of young shoots. Both metals and drought led to disruption in the content of mineral nutrients (Ca, Mg, Fe). Due to high tolerance to Ni and drought, S. viminalis var. ‘Gigantea’ bears high potential for biomass production on Ni-polluted sites with accompanying metal uptake increased under water deficit.