The Spatial and Taxonomic Structures of Microbial Communities in Dry Steppe Zone Soils of the Selenga Highlands (Western Transbaikal Region)

Abstract

This study is concerned with soil microbial communities within the confines of the dry-steppe zone of the Selenga Highlands. The natural and climate conditions of the region, including a prolonged cold period and the low amount of precipitation and their uneven distribution throughout the growing season, govern the formation of the primarily chestnut soils of light granulometric composition, thin humic horizon, and low contents of humus and nitrogen. This work presents data on seasonal dynamics and spatial structure of microbial communities in the studied soils. The number of various ecological–trophic groups of aerobic chemoorganotrophic bacteria was found to vary between several thousand and several million CFU/g. The population parameters were the highest in second half of summer. The examined soil profiles were rather similar in their trends of spatial distribution of the culturable portion of the microbial community. The highest population parameters were recorded from humic horizons for hydrolytic bacteria and middle horizons for oligotrophic bacteria. The high-throughput sequencing method was used to perform full-profile analysis of the taxonomic structure and diversity in prokaryote communities of the light-humic and chestnut quasi-gley soils. Bacteria were dominant at a level of domains with the archaea level being insignificant. At the level of phyla, the structure of bacterial communities was largely made up of species of Actinobacteria, Acidobacteria, Proteobacteria, Bacteroidetes, Chloroflexi, Verrucomicrobia, and Gemmatimonadetes with actinobacteria and acidobacteria being dominant. Diversity indices were estimated in prokaryote communities from the genetic horizons of the studied soils. The Shannon index and Pielou evenness indices were found to be directly correlated with contents of humus and nitrogen. Assessment of the beta diversity revealed that in the analysis at the level of orders and lower taxonomic ranks, microbial communities formed two nonoverlapping clusters, which clumped humic and mineral horizons of soils.