Metagenomic characteristic of rhizosphere effect on cereals in black and sod-podzolic soils

Сhanges in the composition of microbial communities under the influence of root exudation of plants (rhizosphere effect) is widely reported in the scientific literature. A number of studies clearly show the rhizosphere effect of external factors such as soil type, species and plant variety, etc. The aim of this work is to study the effect of soil type and plant species using modern high-throughput sequencing techniques. This effect has been studied well by foreign counterparts, but such work on Russian soils and crops used in the domestic agro-industry, is carried out for the first time. We used two soils contrasting by their agrochemical parameters, black earth (Voronezh region), and sod-podzolic soil (Pskov region). Rye ( Secale cereale L., k-6469) and wheat ( Triticum aestivum L., k-54609) seeds obtained from VIR collection (St. Petersburg) were grown in a greenhouse on both soils for 42 days. Using NGS-V4 variable region sequenced 16S rDNA gene, microbial community composition in bulk soils and the rhizospheres formed on them was analyzed. Despite the short period of the experiment, clear rhizosphere effect was revealed in both soils. The strongest factor was the type of soil. Communities of bulk soil as well as rhizosphere communities on these soils, were significantly different from each other. Both soils show the same effect in the formation of rhizosphere communities of rye and wheat. Type of plant is the second largest (after the type of soil) factor in determining taxonomic composition of the rhizosphere microbiome. Communities of rye rhizosphere in general are closer to the communities of bulk soils than wheat rhizosphere communities. Also, the rhizosphere communities of rye on sod-podzolic soil according to the cluster analysis are closer in structure to the original communities of the soil. The taxonomic analysis of the communities at the level of phyla revealed several groups. They are most responsible for the rhizosphere effect. Formation of rhizosphere communities was accompanied by an increase in the number of Betaproteobacteria class sequences, while reducing the part of the bacteria of Verrucomicrobia phylum. Significant changes in the community occurred in wheat-cultivated sod-podzolic soil. According to the results of all analyzes, these communities differ significantly from the original communities of soil and rhizosphere communities of rye on sod-podzolic soil. Perhaps this can be attributed to an increased proportion of the genus Flavobacterium (phylum Bacteroidetes ) bacteria in these communities. Using the method of high-throughput sequencing it has been clearly demonstrated the presence of rhizosphere effect on rye- and wheat-cultivated soils, as well as the features of the interaction of individual factors responsible for rhizosphere effect. However, to confirm rhizosphere effect, as well as for more detailed studies of the mechanisms underlying it, it is necessary, in addition to the taxonomic analysis carried out, to elucidate how the rhizosphere microbiome is influenced by the plant exudate composition. To do this a series of model experiments with introduction into the soil of certain root exudate substances of rye and wheat are already scheduled.