The genus Fusarium includes many pathogenic species causing a wide range of plant diseases that lead to high economic losses. In this review, we describe how the Fusarium taxonomy has changed with the development of microbiological methods. We specify the ecological traits of this genus and the methods of its identification in soils, particularly the detection of phytopathogenic representatives of Fusarium and the mycotoxins produced by them. The negative effects of soil-borne phytopathogenic Fusarium on agricultural plants and current methods for its control are discussed. Due to the high complexity and polymorphism of Fusarium species, integrated approaches for the risk assessment of Fusarium diseases are necessary.

The review summarizes the most relevant microbiological characteristics that can serve as indicators of soil ecological functions: bioresource, phytosanitary, as well as the functions of carbon transformation and plant nutrition. The indices of diversity and taxonomic structure of microbial communities as well as abundance of certain groups of microorganisms are estimated to characterize the bioresource function of soils. The main microbiological indicators of carbon transformation are microbial biomass carbon, the ratio of bacterial to fungal biomasses, soil respiration, enzyme activities, and the rate of soil organic matter decomposition. The appropriate microbiological indicators of the plant nutrition function of soil are the enzyme activities associated with the nitrogen and phosphorus cycles, as well as molecular species-specific markers of arbuscular mycorrhiza. Gene abundances of phytopathogens and their antagonists can serve as indicators of soil phytosanitary function. Since a high variation of some characteristics and certain difficulties in their interpretation are currently the relevant problems in microbiological indication of soil functions, the key goal is a careful selection of the parameters with the best applicability as indicators of soil ecological functions.

Agricultural practices significantly impact soil properties and ecological functions, highlighting the importance of comprehensive soil health assessments. Traditionally, these assessments have focused on physical and chemical indicators, often neglecting microbiological properties. This review explores the potential of microbiological indicators in evaluating the effects of agricultural practices on soil ecological functions, emphasizing their significance and addressing challenges associated with their application. A key advantage of microbiological indicators is their high sensitivity and rapid response to environmental changes. These indicators can be grouped into three categories: microbial biomass and abundance, microbial taxonomic composition and diversity, and microbial activity. Among these, microbial biomass carbon, basal respiration, and decomposition rates are considered the most reliable and interpretable indicators. Microbial taxonomic composition and diversity remain limited in their diagnostic and predictive capabilities due to challenges in interpretation. Integrating microbiological indicators offers a more holistic understanding of the interactions between agricultural practices and soil health, enhancing our ability to monitor, manage, and preserve soil ecosystems. To facilitate their adoption in agricultural production and land management, further efforts are needed to improve the interpretability of these indicators and to establish standardized criteria for soil health assessment.

The aim of this analytical review is to systematize information on the quantitative characteristics of variation in the content and stock of organic carbon (C_org) in soils. The review considers the estimates for validity and reproducibility of determined C_org values, as well as the spatial variation and heterogeneity of C_org at different hierarchical levels of the soil cover composition and their changes in time. The most powerful factor of C_org changeability in soils is spatial variation. The absolute standard deviation and coefficient of variation for C_org content and stock in soil shows the trend of an increase with the logarithm of the examined plot area. This trend is observed on the background of a wide range of the values of the indicators of spatial C_org variation in each narrow range of the plot area, which leads to a high uncertainty of the estimates with an increase in the area coverage. Direct dry combustion is considered the preferable method among the methods used to determine C_org content. This method gives valid (i.e., with the least biases) and well reproducible data. The indirect Tyurin and Walkley–Black methods systematically underestimate the C_org content and their reproducibility is comparable to the amplitude of seasonal dynamics and minimum spatial variation indices within an elementary soil area. The estimates for the long-term trend of C_org content require strict adherence to stringent monitoring conditions over the time intervals longer than 15 years. The spatial variation in C_org stock is more pronounced as compared with C_org content, which further increases the requirements to monitoring.

The biomass of prokaryotes and fungi, organic carbon stocks, and CO₂ emission were studied in the Cryosols and Leptosols of Franz Josef Land. The highest carbon stocks were found in the Eutric Leptosols (Loamic, Humic) formed in the wind-sheltered areas (23.2 kg C/m² in the upper 50 cm), as well as in Turbic Cryosols (Humiс) that contained organic matter buried by cryoturbation (13.7–20.7 kg C/m²). The number of prokaryotes varied between 0.14 and 2.10 billion cells/g of soil, and the maximum values of their biomass were found in the litter. The fungal biomass varied from tens to hundreds of mg/g of soil depending on the type of soil and biotope. The share of spores was more than a half of the total fungal biomass in 80% of cases. Spores and mycelium were mainly represented by small forms with a diameter of up to 2–3 microns. The length of the fungal mycelium ranged from 4 to 272 m/g of soil. The maximum development of fungi was observed in the lichen biocrusts and moss litters. The fungal biomass decreased exponentially with the depth of horizons, and at the same time the share of prokaryotes in microbial biomass increased by several times. The share of microbial carbon in the total organic carbon was higher in soils of barrens (the most extreme habitats among the studied ones) as compared with the soils of local tundra areas (12.7 versus 2.5%, respectively). The levels of СО₂ emission from the surface of undisturbed soils varied in the range of 1.6–91.7 mg C–CО₂/m² per hour and differed by tens of times between barrens and tundra areas. The studied soils are close to the soils of the Arctic tundra when compared by their carbon stocks and CO₂ emission values; however, their microbial biomass values and their distribution are close to the soils of Antarctica and hot deserts.

The method of luminescent microscopy has been applied to study the structure of the microbial biomass of soils and soil-like bodies in East (the Thala Hills and Larsemann Hills oases) and West (Cape Burks, Hobbs coast) Antarctica. According to Soil Taxonomy, the studied soils mainly belong to the subgroups of Aquic Haploturbels, Typic Haploturbels, Typic Haplorthels, and Lithic Haplorthels. The major contribution to their microbial biomass belongs to fungi. The highest fungal biomass (up to 790 μg C/g soil) has been found in the soils with surface organic horizons in the form of thin moss/lichen litters, in which the development of fungal mycelium is most active. A larger part of fungal biomass (70–98%) is represented by spores. For the soils without vegetation cover, the accumulation of bacterial and fungal biomass takes place in the horizons under surface desert pavements. In the upper parts of the soils without vegetation cover and in the organic soil horizons, the major part (>60%) of fungal mycelium contains protective melanin pigments. Among bacteria, the high portion (up to 50%) of small filtering forms is observed. A considerable increase (up to 290.2 ± 27 μg C/g soil) in the fungal biomass owing to the development of yeasts has been shown for gley soils (gleyzems) developing from sapropel sediments under subaquatic conditions and for the algal–bacterial mat on the bottom of the lake (920.7 ± 46 μg C/g soil). The production of carbon dioxide by the soils varies from 0.47 to 2.34 μg C–CO₂/(g day). The intensity of nitrogen fixation in the studied samples is generally low: from 0.08 to 55.85 ng С₂Н₄/(g day). The intensity of denitrification varies from 0.09 to 19.28 μg N–N₂O/(g day).