Changes in the Toxic Effect of Cadmium on Spring Barley Depending on the Moisture Content of the Soil Substrate

In a greenhouse test, when growing spring two-row barley on sod-podzolic soil and introducing Cd into it at doses of 25 and 45 mg/kg, the toxic effect of cadmium on plants was revealed. The test was carried out under conditions of controlled soil moisture, which was maintained at levels of 45, 50, 55, 60, and 65% of the full moisture capacity (FMC), depending on the variant. Morphometric parameters (appearance, height of plants, their biomass, and leaf area), biochemical parameters (accumulation of MDA, total antioxidants and lipids), and crop structure (weight of straw, weight of grain, thousand-grain weight) were evaluated in test plants. In addition, the total content of heavy metals (HM) and other elements in the soil and their transition to the soil solution were estimated. It was demonstrated that the effects of cadmium stress on spring barley plants of the Zaersky 85 variety underwent significant changes depending on soil moisture. In general, with average humidity values (55-60% FMC) toxic stress was least pronounced, and with a cadmium dose of 25 mg/kg the considered indicators more or less approached the control. A cadmium dose of 45 mg/kg had a suppressive effect on plants in any case; however, maintaining optimum moisture content also contributed to a noticeable reduction in toxic effects. At the same time, with the lowest humidity (45% FMC) the plants with both doses of cadmium under consideration showed signs of serious suppression of all vital signs. A similar pattern, though to a somewhat lesser extent, was noted for excessive soil moisture (65% FMC). This was due to the fact that in such conditions plants experienced joint stress caused not only by the presence of xenobiotics in the soil environment, but also by insufficient or excessive moisture. Thus, according to the sum of the considered indicators, the optimum moisture content for growing barley plants, at which the plant body is in the best shape and is able to most effectively withstand environmental stresses of various nature, should be considered 55% FMC.