Natalia Viktorovna Kostina

For the first time, a comprehensive study of the biological activity of microbial communities in protected tropical ecosystems of Vietnam has been conducted using the example of four types of substrates: mineral soils and associated plant litter, rhizospheric soil, and specific soil-like formations —“suspended” soils in baskets of epiphytic ferns. It is shown that suspended soils and plant litter are characterized by 3‒5 times higher microbial biomass (up to 1.44 mg•g⁻1), as well as significantly more intensive processes of carbon dioxide emission, nitrogen fixation and denitrification compared with mineral soil horizons. The revealed high biological activity of these substrates correlates with an extremely high content of organic carbon (up to 51.4%) and less acidic pH values. For the first time, methane emissions were quantified for this territory, showing maximum values in the upper soil layer (up to 173 ng CH4•g‒1•day–1) and a negative correlation with altitude (p=0.0001). The data obtained make it possible to identify plant litter and epiphytic “suspended” soils as key loci of biogeochemical cycles of nitrogen and carbon in the tropical forests of Vietnam.

We obtained data on the number of saprotrophic bacteria and the structure of bacterial complexes of cultivated bacteria of the soil of the fallow field, the material of anthills located in the field under study, and ants of the species Lasius niger and Lasius flavus, which are dominant species in this fallow field. It has been established that ants of two closely related species from the genus Lasius differ significantly in the number and composition of the cultivated bacteria associated with them, and have a different effect on the microbiocenosis of the soils they inhabit. A high similarity of bacterial complexes of L.niger ants and the material of their nests was shown, at the same time, such a pattern was not revealed for L. flavus. It has been established that the structural components of anthills differ in the number and composition of cultivated bacteria. It has been shown that in general, anthills are loci of increased abundance and higher bacterial diversity compared to control soils, which can be traced not only in the surface soil layer. It has been found that the nesting activity of ants promotes the redistribution of microorganisms down the profile, as a result of which the increased biodiversity of microorganisms is maintained at a greater depth than in the control. To a greater extent, this phenomenon is characteristic of soil-dwelling ants L. flavus. In anthills, an increased number of fertility-improving bacteria with high biotechnological potential, such as Pseudomonas koreensis, capable of fixing atmospheric nitrogen, and Paenibacilluschitinolyticus, showing chitinolytic activity, was found compared to control. According to the results of additional studies, representatives of Agrobacterium radiobacter, not identified by direct inoculation, were identified from the accumulation culture on Ashby's nutrient medium. With the help of genome-wide sequencing, several species of bacteria were identified that were not determined by mass spectrometry.

Despite the significant role of the black garden ant (Lasius niger) in soil formation processes, the seasonal dynamics of microbial biomass in its nests and adjacent urban soils remains poorly understood. The relevance of this study is related to the need to assess the contribution of L. niger to the biological activity of soils under anthropogenic stress. The study is aimed at analyzing the dynamics of microbial biomass and its activity in the nests of L. niger ants and the surrounding urban soils during the growing season. In this work, methods of luminescent microscopy were used to estimate the total number of microorganisms and the dynamics of its changes during the growing season, as well as the method of multisubstrate testing to determine the functional diversity of microbial communities and methods of mathematical statistics. In the studied urban soils, there was a significant decrease in the proportion of fungal and an increase in the proportion of bacterial components in microbial biomass compared to zonal soils. The predominance of fungal cells (spores and yeast cells) was recorded in the fungal biomass, while their maximum number and minimum biomass of fungal mycelium were noted at the end of the growing season. The effect of L. niger ants on the composition of microbial biomass in the soil was manifested in an increase in the length of the fungal mycelium and bacterial biomass reserves compared with the control. The influence of anthropogenic stress on the structure of microbial biomass in anthills is more pronounced than in control soils. The nesting activity of ants had a significant impact on the functional parameters of microbial communities formed in the soil. The material of the anthills showed a change in the spectrum of organic substrates consumed by the microbial complex and the rate of their consumption compared to the control soils. It was found that microbial communities less climactic than in the soil form in anthills in areas with the lowest anthropogenic load, which may be due to a more intense foraging activity of insects in these areas. It should be noted that the stability index (d) of microbial complexes in anthills showed less variability during the growing season than in the same indicator in soils.