No 9 (2025)

The very first Earth`s terrestrial ecosystems – biocrusts and microbial soils – appeared in Archean. The Proterozoic weathering crust (WC) in Pavlovsk granite quarry (Voronezh region) has the inclusions of granite corestones. WC is directly covered by Mid Devonian deposits. The corestones are surrounded by concentric typically multilayered sheets – rindlets (or crusts). More than 40 specimens of such crusts have been collected and analyzed in detail. Typically, they consist from three layers, some – from two or four with a whole thickness from 4 to 20 cm. XRD data showed that unweathered granite, saprolite (material of WC) and studied corestone crusts consist from quartz, microcline, biotite and kaolinite in different proportions. The obtained data show that crusts contain organic C (0.1–0.5%) and are characterized by the elevated concentrations of Fe, Mg, Mn, Ti, P, S, К. Their layered structure is accompanied by the differentiation of properties: chemical, mineralogical and magnetic. The surface layer is enriched in Fe, Mg, Mn, S and depleted in Al, Si, P, Na. SEM study showed the presence of neo formed silicates (kaolinite and sanidine), gibbsite, Ti-oxides, gypsum. Mossbauer spectroscopy demonstrates the presence of oxides including magnetite, Fe-sulphates, pyrite. SEM study showed the variety of fossilized microbiota: solitary cells of coccoidal shape and their colonies (cyanobacteria?), spores, green algae et al. The obtained data allowed to conclude that rindlets are insitu developed soil like biogenic bodies – microbial paleosols. Their macroscale development and horizontal stratification could say about the long duration (n × 10⁴ years) of terrestrial stage which preceded the formation of Mid-Devonian cover.

One of the most informative methods for studying the effects of climate change on the productivity of terrestrial ecosystems is the implementation of in situ manipulative experiments. An alternative to costly and labor-intensive manipulative experiments involving soil warming and drying soil is the monitoring of test plots located near gas flares. The aim of the study was to determine the effect of long-term warming and drying on the kinetics of soil organic matter (SOM) decomposition, microbial biomass C content, and the structure of the soil microbial community at a monitoring research plot near gas flares located in the Khanty-Mansi Autonomous Area (Yugra). Besides, we estimated the stability of previously identified microbial activity indices in response to drying and warming after five years of measurements. A consistent trend of decreasing microbial biomass carbon content, water-soluble forms of nutrients, as well as basal respiration activity, was observed closer to the flare. However, after five years, the previously identified trend of increasing the kinetic rate constant of SOM decomposition (k₁) decreasing the size of the labile SOM pool (A₁) under intensified stress reversed. Changes in the k₁ and A₁ response were probably related to the accumulation of stable SOM fractions and the leveling of productivity and rhizodeposition activity of young pine trees, possibly indicating an “aging” process of the ecosystem. Shifts in the structure of the soil prokaryotic community near the flare were characterized by an increase in the relative abundance of the drought-resistant class Ktedonobacteria (phylum Chloroflexi) and a decrease in the relative abundance of the phyla Acidobacteria, Verruсomicrobia, and archea Thaumarchaeota. For the soil fungal community, increased warming and drying stress led to a rise in the relative abundance of the class Leotiomycetes (phylum Ascomycota) and a decrease in the representation of Agaricomycetes (phylum Basidiomycota). Thus, long-term soil warming and drying results in changes in the composition of the soil microbiome and a significant decrease in microbial biomass, labile carbon and its decomposition rate in the soils of forest ecosystems.