Assessment of the Modifying Effect of Zinc and Copper on Toxic Stress of Barley Plants Caused by Cadmium

In a vegetation experiment on sod-podzolic sandy loam soil with Cd²⁺ addition at doses of 25 and 45 mg/kg, we studied how the response of barley plants to the toxic effects of cadmium changes if various amounts of heavy metals (HM) with the functions of trace elements were introduced together with it, using the example of zinc and copper. In addition, several variants were laid, in which copper and zinc were also introduced along with cadmium. Thus, doses and combinations of metals were used in the experiment: Cd₄₅, Cd₂₅Cu₅₀, Cd₂₅Cu₁₀₀, Cd₂₅Cu₁₀₀, Cd₂₅Cu₂₀₀, Cd₄₅Cu₅₀, Cd₄₅Cu₁₀₀, Cd₄₅Cu₂₀₀, Cd₄₅Zn₅₀, Cd₄₅Zn₁₀₀, Cd₄₅Zn₁₅₀. Morphometric parameters (appearance, height of plants, their biomass and leaf area), biochemical parameters (accumulation of MDA, total antioxidants and crude protein), crop structure (straw weight, grain weight, 1000 grain weight) were evaluated in experimental plants. In addition, the gross content of HM and other elements in the soil and their transition to the soil solution were analyzed. It is shown that the introduction of cadmium alone led to a significant inhibition of the growth and development of barley plants. At the same time, the combined addition of HM trace elements with cadmium significantly modified the effect of cadmium. Zinc contributed to a decrease in the toxic effects of cadmium, and the intensity of this effect increased as the concentration of zinc increased, and the toxic effects of this HM at the doses considered had not yet manifested themselves. Copper, as a more toxic element, showed its stimulating effect at lower doses than zinc, and at higher doses, the development of acute stress caused by the combined toxic effects of 2 HM was observed. This is true for a dose of cadmium of 45 mg/kg, with a lower dose of cadmium (25 mg/kg), copper had a greater stimulating effect. The considered effects were primarily noted when evaluating morphometric indicators and productivity. Based on the biochemical parameters, it was not possible to draw clear conclusions about how the addition of zinc and copper changed the effects of cadmium. Apparently, it was more appropriate to use other biochemical parameters to assess stress effects. It was noted that the introduction of trace elements generally contributed to a reduction in the accumulation of cadmium in the aboveground biomass of barley plants, however, the addition of zinc led to an increased transition of cadmium into straw, but not into grain.