Investigation of the effect of drought stress on bioavailability and bioaccumulation of cadmium, copper, and iron in the Barley

The entry of heavy metals into the soil through fertilizers increases the risk of their transfer to the food chain by changing the pattern of cation accumulation in the plant under the water deficiency. In order to investigate the accumulation of cadmium, copper, and iron by barley, an experiment was conducted as a randomized complete block design with three water deficiency levels (irrigation at 100 (control), 75, and 50% of field capacity) and four sampling stages (each 15 days) in three repetitions in Jiroft region in 2018 and 2019. After harvest, the reduction of soil cadmium, copper, and iron concentrations were 52, 63, and 23%, respectively. Their concentrations in plant shoots were 66, 85, and 96% lower than the ones in roots, respectively. With increasing water deficit, the concentration of residual iron in the soil and shoots increased, and the concentration of copper in soil decreased and increased in roots and shoots, while the cadmium decreased in plant and soil. Copper root accumulation index was higher than one and increased with increasing water deficiency levels, with a significant difference of 6.82 times compared to the control. In the multivariate regression model of growth rate in growth periods, the largest share in explaining the variance of indices belonged to growth rates in the third and fourth fifteen-day periods. According to the regression between growth rate and the indices, with increasing growth rate, the copper accumulation index of roots (β = -0.97) decreased and the translocation index for cadmium (β = 0.83) and copper (β =0.86) increased and for iron (β = -0.94) decreased linearly. In conclusion, under drought stress, none of the studied metals accumulated in the shoots. Although, the concentration of copper in the roots increased 3.31 times as compared to the soil, this increase did not lead any toxicity risk in the shoots.