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Understanding the rate and direction of pyrogenic succession in arid ecosystems, which depends on many factors, including the intensity of grazing and the frequency of pyrogenic expo-sure, will allow for more accurate predictions of the consequences of fire onplant communities, and will assist with better fire management. We studied the vegetation on 55 sites in and near the “Chernye Zemli” Natural Biosphere Reserve that burned at different times or were not affected by fires over the past 35 years and characterized the changes in vegetation cover associated with the impact of wildfire and grazing. The descriptions were grouped into chronological stages according to the time elapsed since the last fire, or into groups according to the frequency of fires. In pairwise comparison of the projective cover of plant species between chronological stages, it correlated most strongly between successive initial stages (for stages 1 and 2, p = 0.003, r = 0.73; for stages 2 and 3, p < 0.001, r = 0.78). Species with an initially higher projective cover were more likely to grow on plots in the first year after the fire: p < 0.03. Plots with rare and frequent fires had similar projective cover of individual species (r = 0.64, p < 0.001). We conclude that in the course of pyrogenic succession, communities are gradually replaced over at least ten years. At the same time, the composition of a plant community at the initial point of succession depends on the prevalence of species in the community before the fire. No fundamental effect of the frequency of fires on the composition of plant communities has been revealed.

The soil response to a jet-fuel contamination is uncertain. In this article, original data on the influence of a jet-fuel spillage on the topsoil properties are presented. The data set is obtained during a one-year long pot and field experiments with Dystric Arenosols, Fibric Histosols and Albic Luvisols. Kerosene loads were 1, 5, 10, 25 and 100 g/kg. The data set includes information about temporal changes in kerosene concentration; physicochemical properties, such as рН, moisture, cation exchange capacity, content of soil organic matter, available P and K, exchangeable NH4+, and water-soluble NO3–; and biological properties, such as biological consumption of oxygen, and cellulolytic activity. Also, we provide sequencing data on variable regions of 16S ribosomal RNA of microbial communities from the respective soil samples.

The article presents protocols for determining the biological activity of kerosene-contaminated soils in terms of two indicators, i.e. cellulolytic activity and biological consumption of oxygen. A method for determining the cellulolytic activity of soils is based on measuring the rate of cellulose decomposition in situ. Model test objects (linen fragments 10 × 20 cm weighing 4–6 g) were put in the root layer of soil. A month later, the linen was removed from soil and its weight loss was measured. Cellulolytic activity was estimated by the weight loss of readily hydrolysable organic matter (RHOM) per day (mg/g RHOM per day). The method for determining the biological consumption of oxygen of water was adapted for soils. The indicator characterizes the ability of microorganisms to oxidize organic substances using oxygen for 5 days. The analytic procedure includes taking a soil sample, preparing the suspension (the ratio of soil to distilled water is at least 1:10) and after 5 days measuring the concentration of unspent dissolved oxygen using the oxygen meter. The proposed methods give reproducible and reliable results on the biochemical activity of soil microorganisms in a wide range of soils, e.g. Retisols, Arenosols and Histosols, including those under hydrocarbon pollution.

One of the most important challenges for soil science is to determine the limits for the sustainable functioning of contaminated ecosystems. The response of soil microbiomes to kerosene pollution is still poorly understood. Here, we model the impact of kerosene leakage on the composition of the topsoil microbiome in pot and field experiments with different loads of added kerosene (loads up to 100 g/kg; retention time up to 360 days). At four time points we measured kerosene concentration and sequenced variable regions of 16S ribosomal RNA in the microbial communities. Mainly alkaline Dystric Arenosols with low content of available phosphorus and soil organic matter had an increased fraction of Actinobacteriota, Firmicutes, Nitrospirota, Planctomycetota, and, to a lesser extent, Acidobacteriota and Verrucomicobacteriota. In contrast, in highly acidic Fibric Histosols, rich in soil organic matter and available phosphorus, the fraction of Acidobacteriota was higher, while the fraction of Actinobacteriota was lower. Albic Luvisols occupied an intermediate position in terms of both physicochemical properties and microbiome composition. The microbiomes of different soils show similar response to equal kerosene loads. In highly contaminated soils, the proportion of anaerobic bacteria-metabolizing hydrocarbons increased, whereas the proportion of aerobic bacteria decreased. During the field experiment, the soil microbiome recovered much faster than in the pot experiments, possibly due to migration of microorganisms from the polluted area. The microbial community of Fibric Histosols recovered in 6 months after kerosene had been loaded, while microbiomes of Dystric Arenosols and Albic Luvisols did not restore even after a year.