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Drought Differently Modifies Tolerance and Metal Uptake in Zn- or Cu-Treated Male and Female Salix × fragilis L.
The aim of this study was to determine the tolerance to metals (Zn, Cu) and drought of male and female Salix × fragilis L. under isolated and combined treatments, and to assess the metal uptake and profiling of metabolic plant responses. The 14-day experiment was performed in a hydroponic system, and metals were applied at 1.5 mM in a Knop’s solution. Drought simulation was achieved by adding sorbitol at a moderate level (200 mM). Isolated Zn treatment enhanced plant growth, more pronouncedly in females. Equimolar Cu treatment caused diverse reactions, and females exhibited significantly higher tolerance. Male specimens were less tolerant to isolated drought and to combined drought and metal presence. The highest contents of Cu and Zn were found in roots, compared to the aboveground tissues (wooden rods and leaves), of both female and male metal-treated plants. Simultaneously applied drought limited Zn accumulation in roots and elevated its translocation to leaves while increasing Cu accumulation, predominantly in females showing higher tolerance. Both isolated and combined drought and metals reduced leaf water content, caused the allocation of mineral nutrients (Ca, Mg, K, and Na), and affected metabolism in a stressor-specific and sex-dependent manner. For males, Cu accumulation in the leaves was significantly correlated with the majority of metabolites, while for both sexes, kaempferol and salicylic acid were strongly correlated, indicating their role in tolerance against the metal. The obtained results are an excellent starting point for the practical use of male and female Salix × fragilis L. in areas heavily polluted with Cu or Zn and exposed to drought, for the purpose of their recultivation.
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.