Precipitation pattern during warm and cold periods in the Bronze Age (around 4.5-3.8 ka BP) in the desert steppes of Russia: Soil-microbiological approach for palaeoenvironmental reconstruction

A comparative analysis of the chemical and microbiological properties of palaeosols buried beneath burial mounds (kurgans) of the Bronze Age in the desert steppe zone of Russia provides an opportunity to elucidate the precipitation pattern during cold and warm seasons. Soil salinity in the desert steppes depends on the amount of precipitation during the cold season. Snow melting provides a deep drenching of soil and leaching of toxic salts down the profile. Summer precipitation moistens several upper inches of the soil but does not affect its general chemical properties. At the same time, the state of soil microbial communities is influenced by the spring-summer moisture. The more precipitation there is during the vegetation period, the more phytomass there is, and therefore, more plant residues enter the soil, thereby causing an increase of the microbial biomass that decomposes it. The results of the study of subkurgan palaeosols buried about 4200-3900 yr BP in the desert steppe zone in the southeast of the Russian Plain show an increase of soil salinity with a simultaneous increase in the microbial biomass and number of cells that are decomposing plant residues. The hypothesis of a reduction in winter precipitations and an increase in precipitation during the warm season is assumed. These findings explain a bloom of archaeological Middle Bronze Catacomb culture in the desert steppes. The lack of snow and increased precipitation during the vegetation season affected the productivity of phytocenoses and prevented spring burns of vegetation, which provided more favourable conditions for the early cattle breeders of the catacomb Bronze Age population.