Influence of heavy metals pollution on the formation of microbial community in gray forest soil

Abstract

The state of microbial communities in gray forest soil contaminated with heavy metals at a dose of 5, 10, 100 MPC, in the presence and absence of vegetative phytosynesis (corn) has been investigated in model experiments. The protective function of the phytocenosis concerning several groups of microorganisms, in particular, azotobacter and polysaccharide-synthesizing bacteria, has been shown. The number of azotobacter in the rhizosphere of plants exceeds the indices of soil without plants: in the control by 3.33%, at 5 MPC – 36.6, at 10 MPC - by 95.6%. The indicative function of azotobacter has been confirmed concerning soil pollution with heavy metals. The number of azotobacter is decreased with increasing the pollutant dose in the soil without plants: at 5 MPC - by 2.64 times, at 10 MPC - by 6.67 times, the corresponding indicators for plants rhizosphere are 2.05 and 3.52 times. Azotobacter is not detected by the method of overgrowing soil lumps at the maximum level of soil contamination with heavy metals (100 MPC). The mycelial forms of microorganisms (micromycetes) are highly resistant to contamination with heavy metals that have been confirmed. The activity of mineralization of organic substances, including hummus, is decreased with the increasing of pollutant dose in the soil has been shown. The pedotrophy index decreases at 5 MPC by 3.16%, at 10 MPC - 30,9, and 100 MPC - by 46.8% in soil without plants. Similar numbers for variants with plants fluctuate between 14.2 and 105.4%. The conclusion about a lesser susceptibility to microbial mineralization of complexes of humic acids and heavy metals has been confirmed. With an increase in the dose of the pollutant, the activity of humus mineralization decreases in soil without plants: at 5 MPC - by 16.7%, at 10 MPC – 12.6, at 100 MPC - by 74.7%; with plants: at 5 MPC - by 14.3%, at 10 MPC – 8.33, at 100 MPC - by 113.7%. It is also drawn attention to the fact that the activity of humus mineralization in the soil rhizosphere is lower than in the soil without plants. In our opinion, the reason for this is the presence of easily utilized substrates in the composition of plant root exudates. It makes the mineralization of hard-to-reach humus molecules inappropriate.