Effect of an Equal Dose of Polymetallic Pollution on the Microbiological Characteristics of Two Soils with Different Organic Carbon Contents

Reliable stable indicators are very important for assessing soil quality. This paper compares the dynamics of microbial parameters in two different soils (rich/poor in organic carbon), contaminated in laboratory experiments with an equal dose of heavy metals (HMs) after 30 and 90 days. For this purpose, the changes in the number, biomass, and taxonomic structure of bacterial and fungal communities were assessed in microcosm experiments using an organic carbon–rich ordinary chernozem (Ch-humus-rich soil) and a depleted carbon agrozem (Ag-humus-poor soil), spiked with high concentrations of a zinc, lead, and copper solution (1100 Zn + 660 Cu + 650 Pb mg per kg soil). At the 30th and 90th day from HM contamination, soil samples were collected for analyzing microbial community lipid markers by gas chromatography-mass spectrometry. The results show how both biomass and taxonomic structure of the bacterial and fungal communities analyzed were differently sensitive to HM contamination, depending on the type of soil. The Ag-humus-poor soil microbial community was significantly affected by the HM pollution with an increase in both fungi and bacteria and inside the latter several species changed their percentages. Differently, the Ch-humus-rich soil microbial community was not influenced by the HM addition. However, the negative impact of HM can manifest itself over time, so the microbial structure and its functioning cannot represent accurate indicators of the quality of all soil types. The results show that microbial characteristics should be taken into account only in a comprehensive assessment of soil quality in accordance with ISO 19,204:2017—soil quality TRIAD approach. This approach to environmental risk assessment combines biological data (from bioassay and ecological observations) with chemical analysis.