Distribution of prokaryotic communities throughout the Chernozem profiles under different land uses for over a century

Land use affects physical, chemical and biological properties and processes in soil. Long-term field experiments were employed to reveal changes of soil characteristics induced by land use. Using high-throughput 16S rRNA gene amplicon sequencing and quantitative PCR, comparative analyses were conducted on prokaryotic community structure in different soil diagnostic horizons of Chernozems under forest, fallow and arable land within a long-term field experiment established by V.V. Dokuchaev in 1892. Soil organic carbon (SOC) was a more sensitive and reliable indicator of changes than microbial diversity indexes. Verrucomicrobia changed most among different prokaryotic phyla. Long-term tillage did not result in detectable changes in α-diversity of Chernozem prokaryotic communities, except for that plow pan horizon that showed a pronounced decrease in microbial diversity. The differences in prokaryotic community structure between soil horizons were more contrasting than between land uses. Analysis of β-diversity indicated that soil microbial communities at different depths formed non-overlapping clusters of A and B horizons, while microbiomes of transitional AB horizons fall in between these two clusters. The sharp decline in α-diversity in the plow pan horizon, as well as significant differences between the communities of A and B horizons indicate that the soil microbiomes are horizon-specific.