Sergey Ilyich Kolesnikov

The number of soil bacteria is an indicator of the condition and health of soils under chemical contamination. However, the native abundance of soil bacteria in the soils of different climatic zones varies significantly. Depending on the soil-forming factors, the number of bacteria in the soils of different climatic zones will vary. To assess changes in the number of soil bacteria, soil contamination of different climatic zones (semi-deserts, steppes and forests) with lead (Pb) in the following concentrations was modeled: 100, 1000 and 10,000 mg Pb×kg^–1 of soil. It was found that at a maximum concentration of 10,000 mg Pb×kg^–1 of soil, the number of soil bacteria in different types of soils was inhibited by 46–92% compared with the control. With an increase in Pb concentration, the number of soil bacteria decreased in semi-desert soils: from 1.61 billion×g^–1 (typical salt marsh) to 0.89 billion×g (chestnut and brown semi-desert soils); in steppe soils: from 4.50 billion×g^–1 (podzolic chernozem) to 0.80 billion×g^–1 (common chernozem); in forest soils: from 8.00 billion×g^–1 (dark gray forest soil) to 1.90 billion×g^–1 (sod-podzolic soil). The soils of the forest climate zone were found to be the most resistant to Pb pollution, while the soils of the steppe climate zone were the least resistant. Among semi—desert soils, the most sensitive are typical salt marshes, among steppe soils — podzolic chernozems, forest soils - sod-podzolic illuvial-ferruginous soils. A comparison of the number of soil bacteria in three climatic zones of Russia with lead contamination has been carried out. The results of the study can be used to indicate the ecological status and health of soils contaminated with heavy metals.