Microbial Communities of Interglacial and Interstadial Paleosols of the Late Pleistocene

The taxonomic structure of microbial communities in the Late Pleistocene paleosols of different ages in the Central Russian Upland formed under contrasting climatic conditions were analyzed. The humic horizons of paleosols in the interstadial periods of the Early Valdai (105–95 kyr ago), Middle Valdai (33–24 kyr ago), Mikulino interglacial (130–117 kyr ago), and of the modern (Holocene) chernozem were considered. Microbial DNA was analyzed using quantitative PCR and 16S rRNA gene amplicon sequencing (DNA metabarcoding). The numbers of copies of archaeal, bacterial, and fungal genes gradually decreased with an increase in the soil age. All considered paleosols significantly differed from one another in the structure of their microbial communities. The Verrucomicrobia-to-Nitrospirae ratio was used as a diagnostic parameter reflecting the organic matter supply and the changes in carbon and nitrogen cycles. The Verrucomicrobia-to-Nitrospirae ratio in the interstadial soils was 140–200 times lower as compared with that in the modern soil (typical chernozem) and in the paleosols of the Mikulino interglacial. The share of gram-negative Proteobacteria and Acidobacteria increased with the soil age, whereas the share of gram-positive Actinobacteria and Firmicutes decreased. The modern chernozems and interglacial paleosols were characterized by similar values of microbial diversity, while the paleosols of the Valdai interstadial had significantly lower microbial diversity and species richness. Analysis of β-diversity showed that the paleosols of different types and ages maintained the difference in the structure and diversity of their microbial communities depending on the conditions of their formation. Thus, the microbial communities can be used as potential stratigraphic markers and indicators of different climatic conditions, under which the given paleosols were formed.