Microbiological Indicators of Heavy Metals and Carbon-Containing Preparations Applied to Agrosoddy-Podzolic Soils Differing in Humus Content

The response of the microbial community (microbial biomass carbon (Cmic), basal respiration (BR), and functional diversity (FD)) of agrosoddy-podzolic soil (Albic Glossic Retisols (Loamic, Aric Cutanic, Ochric)) to pollution by heavy metals (HMs: Cu 660, Zn 1100, Pb 650 mg/kg) and carbon-containing preparations (5% of biochar and 0.25% of lignohumate) was studied in model experiment (30 days). Soils with different organic carbon contents (Corg 3.86 and 1.30%) were sampled at two sites (Chashnikovo, Moscow oblast). We determined Cmic by the substrate-induced respiration method and FD by multisubstrate testing (47 substrates). It was found that HMs application reduced Cmic on average by 49–57%, BR by 23–52%, and FD by 45%, but, on the contrary, increased the microbial metabolic quotient (qCO2 = BR/Cmic) by 9–46%. The changes of these properties were most significant in the soil with low Corg content (1.30%). Carbon-containing preparations did not contribute to variations in Cmic, BR, and qCO2 in both soils with HMs, but increased their FD. It is concluded that the studied microbiological parameters may be used as indicators for optimal assessment of soil quality: FD and Cmic are the more sensitive to HMs than BR and qCO2.