Effect of lead on growth characteristics of microorganisms in soil and rhizosphere of Dactylis glomerata

The effects of lead oxide and lead nitrate on the growth strategies of microbial communities in the soil and in the rhizosphere of orchard grass (Dactylis glomerata L.) were studied. The maximum specific growth rate of the microorganisms (μ_m) changed significantly when the concentration of mobile forms of lead in the soil exceeded 170 mg Pb/kg, which corresponded to the addition of 400–1000 mg Pb/kg of soil in the form of lead nitrate. The addition of lead resulted in the suppression of a part of the r-strategists and in the more active development of the K-strategists in the adapted microbial community. It was demonstrated that the community of rhizosphere microorganisms could be a more sensitive indicator of lead pollution than the nonrhizosphere microbial community. The values of the auxotrophy index (the ratio between the μ_m values upon the growth on glucose and yeast extract) demonstrated a tendency towards a decrease in the metabolic diversity of the soil microbial community under the impact of lead.