Estimation of the total and active microbial biomasses in buried subkurgan paleosoils of different age

Microorganisms that were isolated from steppe soils buried below kurgans from 5800 to 750 years ago were analyzed for the completeness of isolation, total biomass (the sum of glucose-reactivated and resting microbial cells), and active biomass (metabolically active cells). The metabolic state of microbial communities in buried and modern background soils was estimated from the proportion of active and total biomasses. The paleosoils were found to be characterized by lower total and active biomasses and a lower proportion of active microorganisms as compared to the modern background soils. The age-dependent decrease in the content of active microorganisms in the microbial communities of paleosoils was not monotonic. For instance, the 4000-year-old paleosoil was characterized by a high total biomass and a relatively low content of active microorganisms, whereas the 1950-year-old paleosoil was characterized by a relatively low total biomass and a relatively high content of active microorganisms. This could reflect the temporal dynamics of paleoclimatic conditions in the geographic region under study.