Phytotoxicity of Heavy Metals in Contaminated Podzolic Soils of Different Fertility Levels

We have compared the impact of heavy metals (HMs: Cu 660 + Zn 1100 + Pb 650 mg/kg) on agrosoddy-podzolic soils (Albic Retisols (Loamic, Aric, Cutanic, Ochric)) of two arable fields (Chashnikovo, Moscow oblast) with different contents of organic carbon (Corg 3.86 and 1.30%) and different fertility levels using indicators of acute and chronic phytotoxicity. At the same level of polymetallic contamination, the responses of test plants to the presence of high concentrations of HMs and potential remediants (lignohumate and biochar) in soils of the same type with different Corg contents noticeably differ with respect to plant growth parameters and metal accumulation in the phytomass. The HMs contamination of low-fertile soil leads to the complete death of plants in the pot experiment, while plants on highly fertile soil continued to develop until flowering with only slight deviations from the control. Experimental data on the contents of total and water-soluble forms of HMs and nutrients in the studied soils are presented. The relationships between the chemical composition of soils and the results of phytotests have been found using the principal component analysis. It is shown that the threefold difference in the content of Corg between the soils of the same texture and acidity (pH) result in significantly different response of test plants to the same concentration of HMs. The necessity of correcting the standards for the permissible concentration of HMs in soils with due account for the Corg content in addition to pH and texture is discussed.