State of microbial communities in paleosols buried under kurgans of the desert-steppe zone in the Middle Bronze Age (27th–26th centuries BC) in relation to the dynamics of climate humidity

The size and structure of microbial pool in light chestnut paleosols and paleosolonetz buried under kurgans of the Middle Bronze Age 4600–4500 years ago (the burial mound heights are 45–173 cm), as well as in recent analogues in the desert-steppe zone (Western Ergeni, Salo-Manych Ridge), have been studied. In paleosol profiles, the living microbial biomass estimated from the content of phospholipids varies from 35 to 258% of the present-day value; the active biomass (responsive to glucose addition) in paleosols is 1‒3 orders of magnitude lower than in recent analogues. The content of soil phospholipids is recalculated to that of microbial carbon, and its share in the total soil organic carbon is determined: it is 4.5–7.0% in recent soils and up to three times higher in the remained organic carbon of paleosols. The stability of microbial communities in the B1 horizon of paleosols is 1.3–2.2 times higher than in the upper horizon; in recent soils, it has a tendency to a decrease. The share of microorganisms feeding on plant residues in the ecological–trophic structure of paleosol microbial communities is higher by 23–35% and their index of oligotrophy is 3–5 times lower than in recent analogues. The size of microbial pool and its structure indicate a significantly higher input of plant residues into soils 4600–4500 years ago than in the recent time, which is related to the increase in atmospheric humidity in the studied zone. However, the occurrence depths of salt accumulations in profiles of the studied soils contradict this supposition. A short-term trend of increase in climate humidity is supposed, as indicated by microbial parameters (the most sensitive soil characteristics) or changes in the annual variation of precipitation (its increase in the warm season) during the construction of the mounds under study.