Microbiome status and determinants in soils from the region of Maritsa-Iztok coal mine (Bulgaria). II. Spolic Technosols

Venera Tsolova, Kostadinka Nedyalkovа, Plamen Tomov and Victor Kolchakov
Institute of Soil Science, Agrotechnologies and Plant Protection “N. Poushkarov”, 1331 Sofia, Bulgaria


Tsolova, V., Nedyalkovа, K., Tomov, P. & Kolchakov, V. (2021). Microbiome status and determinants in soils from the region of Maritsa-Iztok coal mine (Bulgaria). II. Spolic Technosols. Bulg. J. Agric. Sci., 27 (4), 727–735

Soil microbial community plays important role in maintaining the soil sustainability and is integrally related to soil fertility since provides the accessibility and cycling of nutrients in organic niches. Different parameters, characterizing the structure and activity of soil microbiome usually serve as indicators for reclamation effectiveness. Among them, the basal soil respiration, microbial biomass carbon content, microbial density and diversity are widely used all over the world as a measure of the progress of bio-transforming processes and the turnover of soil into a functioning ecosystem. Based on these parameters this paper aimed to establish the microbiome status and determinants in natural and reclaimed soils affected by pyrogenic carbon emissions in the area of Maritsa-Iztok lignite basin and particularly to reveal the response of microorganisms to such anthropogenic influence. Pyrogenic carbon (PyC) is a climate-warming agent and its influence on biological and chemical processes in soils is of paramount importance nowadays in view of the amplification of climate changes. In this part of the study, data on three reclaimed soils (Spolic Technosols) located close to Maritsa-Iztok industrial complex are presented.
The results obtained show that the basic feature of studied Tecnosols is the different depth of the humus horizon formed by reclamation and this together with their proximity to the main source of pyrogenic carbon (“Maritsa-Iiztok 2” Thermal Power Plant) determines the observed differences in the activity, density and behavior of different microbial groups. The general hallmark of studied microbial populations was the strong density decrease in sub-horizons, active participation in the biochemical transformations of organic matter, including the stable fraction of PyC and low need of endogenous available nitrogen. Likewise the natural soils oligotrophic, heterotrophic and ologonitrophilic bacteria prevailed in Technosols but mainly oligotrophs and ologonitrophils showed asynergetic behavior in respect of other microorganisms and were capable to utilize the exogenous nutrients equally well. Due to the extremely high spatial variation of oligonitrophils density this group could be used as bioindicator of soil anthropogenization especially of pyrogenic carbon (PyC) accumulation. Only organic carbon, PyC (with small exceptions) and available potassium determined the microbial growth and density in studied Technosols while pH, humic acids, available nitrogen and clay contents were not significant factors. Availablity of phosphorus positively influenced microbiome status only in Technosols occupied by perennial crops (profiles 2 and 3) with exception of asynergetic groups. In low content of organic carbon and prevailing mineralization processes carbonates become important determinant of microbiome activity.

Keywords: Spolic Technosols; microbial biomass; microbial density; pyrogenic carbon; soil nutrients

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