Biomass and Functional Diversity of Microbial Communities in Catenas of Virgin 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 of virgin 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 determination of the content of phospholipids. Multisubstrate testing of respiratory responses in the MicroResp system after the addition of amino acids, carboxylic acids and carbohydrates was carried out. It was established that in the virgin chernozem, microbial biomass decreased in from the watershed towards the accumulative part of the slope; in the gray forest soil, minimal values were in the transit part of the catena. In the plowed horizon of agrochernozems, it was close in all parts of the catena and 2–3.5 times less than in virgin chernozems. For the agro-gray soils, an increase in microbial biomass was fixed in the 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 – 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. In all virgin and arable catenas, an increase in metabolic diversity was noted from the watershed to the accumulative part of the catena. 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 agro-gray soil in the transit part of the catena, where the number of significant responses increased 3.6 times in comparison with the virgin variant.