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Tuesday, July 28 • 17:15 - 17:20
Shifts in the microbial community of soil in long-term burial conditions

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Paloesols (buried soils) are generally formed by covering the undisturbed soil with mounds of different origin. Fresh organic matter is no longer delivered to the buried soil for a long time, as well as humidification, temperature and air regimes changes. This leads to the emergence of various diagenetic processes and shifts in the structure of soil microbiome. Microbial communities of paleosols are considered to be partially conserved and serve as sources of information describing soil conditions before burial, however, this issue is still unclear. On the one hand, a number of chemical and morphological properties and their profile stratification persist in buried soils, on the other hand, a decrease in the number of microorganisms and shifts in the trophic and taxonomic structure of the microbiome are observed. To assess changes in the prokaryotic community during burial, a comparative analysis of the microbiome of the dark chestnut buried under the mound of 500  B.C. and the adjacent surface dark chestnut soil, located in the same landscape conditions, was performed. To scale this difference, other soil types (chernozem, sod-podzol, and gray soil) were taken for comparison. 16S rRNA gene copies abundance was assessed with qPCR, taxonomic structure was analyzed by using throughput sequencing of amplicon libraries of V4 16S rRNA fragments with dada2 package and QIIME2 software.The significance of the differences in representation and abundance of philotypes was assessed with DESeq2 package. Metabolic pathways were reconstructed using Picrust2 software.
The buried soil demonstrated the conservation of the profile stratification with the corresponding differentiation of microbial communities. The decrease in total bacterial number (1.8 - 15.7 times depending on the horizon), as well as significant differentiation between A and B horizons was determined here, in comparison with surface soil.
Significant differences in microbiomes of different horizons were revealed even at the level of phyla (especially Actinobacteria, Proteobacteria, Firmicutes, Thaumarchaeota (Archaea), Acidobacteria, Chloroflexi, Bacteroidetes, Planctomycetes). We determined significant changes in the soil microbiome, and the scale of these changes was comparable with the differences between soils of different types. In the buried soil a decrease in the genus Gaiella, orders Rubrobacterales, Solirubrobacterales, Nitrososphaerales (Archaea), Frankiales, and an increase in the Acidimicrobiia class, phyla Firmicutes (Bacillales) and Chloroflexi were observed. In the upper horizons, the shares of Bacteroidetes and Verrucomicrobia increased. Thus, the burial increases the proportion of microorganisms capable of survival under adverse environmental conditions and the oligotrophic type of nutrition. The presence of microorganisms participating in the nitrogen cycle in the buried soil (Nitrolancea, Candidatus Alisiosphaera, Rhizobiales, Candidatus Nitrososphaera) may indicate that its environment remains stable after burial and maintains the cycle of the main biogenic elements. However, cluster analysis showed that the microbiomes of A and B horizons of the buried soil migrate to the group of C horizons, which may indicate a greater degree of their “mineralization”. This is confirmed by the analysis of potential metabolic pathways showing the predominance of degradation processes in horizons A and B of the buried soil.

This work was supported by the Russian Science Foundation, № 18-16-00073.

Speakers
KA

Kichko A.A.

All-Russian Research Institute for Agricultural Microbiology


Tuesday July 28, 2020 17:15 - 17:20 MSK
Zoom Conference https://zoom.us/j/94321101353?pwd=QlJBb09uM0NVVnVyK0FkbTJ3Nkcrdz09