Humic substances originating from various organic matters can ameliorate soil properties, stimulate plant growth, and improve nutrient uptake. Due to the low calorific heating value, leonardite is rather unsuitable as fuel. However, it may serve as a potential source of humic substances. This study was aimed at characterizing the leonardite-based soil amendments and examining the effect of their application on the soil microbial community, as well as on potato growth and tuber yield. A high yield (71.1%) of humic acid (LHA) from leonardite has been demonstrated. Parental leonardite (PL) and LHA were applied to soil prior to potato cultivation. The 16S rRNA sequencing of soil samples revealed distinct relationships between microbial community composition and the application of leonardite-based soil amendments. Potato tubers were planted in pots in greenhouse conditions. The tubers were harvested at the mature stage for the determination of growth and yield parameters. The results demonstrated that the LHA treatments had a significant effect on increasing potato growth (54.9%) and tuber yield (66.4%) when compared to the control. The findings highlight the importance of amending leonardite-based humic products for maintaining the biogeochemical stability of soils, for keeping their healthy microbial community structure, and for increasing the agronomic productivity of potato plants.

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Coal microbial communities have not been well examined, despite their importance in the formation and maintenance of terrestrial ecosystems. Microorganisms are geographically versatile, exhibit wide morphological diversity and provide a rich platform for studying energy and carbon flows through different ecosystems. The coal characteristics, in turn, are important environmental factors that control the composition, structure and activity of terrestrial bio-communities through various endogenous physiological and biochemical processes. The total phylogenetic structure of prokaryotes is closely related to their functional diversity and, ultimately, to the variety of environmental conditions in oxidized coal (leonardite). Metagenomic studies in this area attempt to assess the relationship between the coal properties and its microbiome. The microbial community of the coal profiles, collected from various Kazakhstan coal deposits, have been studied in detail for the first time using high-throughput sequencing. As part of this study, a wide range of leonardites generated in various bioclimatic and geomorphological conditions are considered. A comprehensive characterization of the phylogenetic structure and diversity of coal was given on the basis of the 16S rDNA gene analysis. The revealed features of the prokaryotic composition can be used as bioindicators of the leonardite condition. In addition, metagenomic characteristics of coals of different origin can serve as valuable platform to assess the terrestrial ecosystem health.

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