Biomass and Functional Diversity of Microbial Communities in Catenas of Reserved and Arable Gray Soils and Chernozems

The biomass and functional diversity of microbial communities were studied in the watershed, transit, and accumulative positions in catenas composed of reserved gray soils (Luvic Retic Phaeozems) and chernozems (Haplic Chernozems) of the Belogorye Nature Reserve and arable variants outside the reserve. Microbial biomass was determined by the substrate-induced respiration (SIR) and the content of phospholipids. Multisubstrate testing of respiratory responses was carried out in the MicroResp system after the addition of amino acids, carboxylic acids, and carbohydrates. It was found that microbial biomass decreased in the reserved chernozem from the watershed towards the accumulative part of the slope; minimal values in the gray soil were recorded in the transit part of the catena. It was close in the plowed horizon of agrochernozems in all parts of the catena and 2–3.5 times less than in reserved chernozems. An increase in microbial biomass was recorded in the agrogray soils of the transit and accumulative parts of the catena. Cluster analysis of respiratory responses in the 0–10 and 10–20 cm layers identified two groups of the most demanded substrates. The first group in both layers included citric and ketoglutaric acids, the second group included fructose and succinic acid. Ascorbic acid, sucrose, and glutamine were included in the first group in the 0–10 cm layer and in the second group (along with asparagine and glycine) in the 10–20 cm layer. An increase in metabolic diversity was observed from the watershed to the accumulative position of the catena in all reserved and arable catenas. At the same time, plowing led to its decrease in the 0–10 cm layer: up to 1.5 times in chernozems and up to 4 times in gray soils. In the 10–20 cm layer, similar trend was observed, except for the agrogray soil in the transit part of the catena, where the number of significant responses increased 3.6 times in comparison with the reserved variant.