Study of rhizospheric microbial communities of plants growing under different environmental conditions is important for understanding the habitat-dependent formation of rhizosphere microbiomes. The rhizosphere bacterial communities of four amaranth cultivars were investigated in a laboratory pot experiment. Amaranthus tricolor cv. Valentina, A. cruentus cv. Dyuimovochka, and A. caudatus cvs. Bulava and Zelenaya Sosulka were grown for six months in three soils with different anthropogenic polyelemental anomalies and in a background control soil. After the plant cultivation, the rhizosphere soils were sampled and subjected to metagenomic analysis for the 16S rRNA gene. The results showed that the taxonomic structure of the amaranth rhizosphere microbiomes was represented by the dominant bacterial phyla Actinobacteriota and Proteobacteria. A feature of the taxonomic profile of the rhizobiomes of A. tricolor cv. Valentina and A. cruentus cv. Dyuimovochka was a large abundance of sequences related to Cyanobacteria. The formation of the amaranth rhizosphere microbiomes was largely unaffected by soils, but cultivar differences in the formation of the amaranth rhizosphere microbial structure were revealed. Bacterial taxa were identified that are possibly selected by amaranths and that may be important for plant adaptation to various habitat conditions. The targeted enrichment of the amaranth rhizosphere with members of these taxa could be useful for improving the efficacy of amaranth use for agricultural and remediation purposes.

In a model experiment, some adaptive characteristics, the bioaccumulation of toxic elements from technogenically-contaminated soils with polyelement anomalies, and rhizosphere microflora of Japanese millet, Echinochloa frumentacea, were studied using biochemical, microbiological, physicochemical (AAS, ICP-MS, INAA), and metagenomic (16S rRNA) methods of analysis. Good adaptive characteristics (the content of photosynthetic pigments, low molecular weight antioxidants) of E. frumentacea grown on the soils of metallurgical enterprises were revealed. The toxic effect of soils with strong polyelement anomalies (multiple excesses of MPC for Cr, Ni, Zn, As, petroleum products) on biometric parameters and adaptive characteristics of Japanese millet were shown. The rhizosphere populations of E. frumentacea grown in the background soil were characterized by the lowest taxonomic diversity compared to the rhizobiomes of plants grown in contaminated urban soils. The minimal number of all groups of microorganisms studied was noted in the soils, which contain the highest concentrations of both inorganic (heavy metals) and organic (oil products) pollutants. The taxonomic structure of the rhizospheric microbiomes of E. frumentacea was characterized. It has been established that E. frumentacea accumulated Mn, Co, As, and Cd from soils with polyelement pollution within the average values. V was accumulated mainly in the root system (transfer factor from roots to shoots 0.01–0.05) and its absorption mechanism is rhizofiltration. The removal of Zn by shoots of E. frumentacea increased on soils where the content of the element exceeded the MPC and was 100–454 mg/kg of dry weight (168–508 g/ha). Analysis of the obtained data makes it possible to recommend E. frumentacea for phytoremediation of soil from Cu and Zn at a low level of soil polyelement contamination using grass mixtures.

Using the INAA method, the ability of Amaranthus tricolor L. variety “Valentina” growing on soils with different degree of pollution to extract heavy metals was evaluated in the field experiments. It was found that amaranth of the studied variety characterized by the content of betacianin pigment, amaranthine, in the shoots and generative organ, is able to accumulate elements such as Mn, Fe and Ni from soils. The content of most of the studied elements decreases in the following order: leaves inflorescences stems. Under conditions of soil pollution with emissions from metallurgical plant, the phytoextraction of such elements as Mn, Fe, Co, Sb increases. The content of Fe and Mn in the leaves of A. tricolor var. “Valentina” exceeds the average data for vegetation from 7 to 17 times; the Co content exceeds the average data for vegetable from 4 to 7 times; the Sb content in the leaves exceeds the average data for vegetable from 10 to 23 times. Due to the fact that amaranth forms a sufficient biomass for the growing season, it can be recommended for phytoextraction of heavy metals from soils in case of polymetallic pollution.

The stimulating effect of humic acids on the processes of growth and development of cress seeds has been revealed. It has been established that use of humic acids of black alder fen peat most effectively affects the sowing qualities of seeds under conditions of oil pollution (an increase in the germination energy and germination capacity compared to the non-humic acid variant by 38%). The minimal inhibitory effect on shoot growth was observed in the soil with hexadecane (20.8 mm less than the control), the maximum – in the soil with oil (22.5 mm less than the control). Humic acids show a stimulating effect on the growth of cress roots under conditions of pollution with oil hydrocarbons. The root length indicators exceeded the values obtained in the version with the pollutant without the use of humic acids from 6% (oil) to 16% of the control (hexadecane). Based on the data obtained during the vegetation experiments, it can be assumed that the stimulating activity of humic acids is more pronounced in stressful conditions for the organism. The biostimulating effect of humic acids was revealed, which manifested itself in an increase in the length of the hypocotyl and root, and the physiological activity of detoxicants was more effectively detected under conditions of pollution with oil hydrocarbons. According to the results of the vegetative experience on a substrate with hexadecane during the irrigation with humic acids of sphagnum high-moor peat, the maximum values of the test responses were determined, corresponding to the control values ​​obtained on the uncontaminated substrate, or higher than the latter. In the variant with oil, the most pronounced effect was achieved with the introduction of humic acids of reed fen and sphagnum high-moor peat, which confirms the hypothesis about the protective effect of humic acids in pollution conditions, which is determined by the binding ability of humic acids in relation to toxicant and their own biological activity in the relation to plants. It is proved that humic acids of peats make a significant contribution to the natural processes of self-purification, causing immobilization and detoxification of petroleum hydrocarbons, which indicates the prospects of their application in technologies of purification and recultivation of polluted water and soil media.