Microbiome status and determinants in soils from the region of Maritsa-Iztok coal mine (Bulgaria) I. Natural soils – Smolnitsas (Pellic Vertisols)

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


Tsolova, V., Nedyalkova, K., Kolchakov, V. & Tomov, P. (2021). Microbiome status and determinants in soils from the region of Maritsa-Iztok coal mine (Bulgaria). I. Natural soils – Smolnitsas (Pellic Vertisols). Bulg. J. Agric. Sci., 27 (4), 719–726

Soil microorganisms rapidly respond to anthropogenic changes and are useful indicators for perturbations in the soil matrix or the reclamation effect on mine spoils. 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 formed during the combustion of fossil fuels or vegetation and has multiple negative impacts on climate, public health and environment. Nowadays its influence on biological and chemical processes in soils is of paramount importance in view of the amplification of climate changes.
In this part of the study two typical for the region natural soils Smolnitsa type (Pellic Vertisol) were analysed. The first soil (profile 1) is situated far from the mining region and hence was chosen for a referent soil. Samples from genetic horizons of soils, as well as from the surface horizon of vulnerable soil (located between the two sources of PyC) were collected by pit trial technique and monitoring approach on 2-th of June 2018.
Data obtained showed that due to the inherent three dimensional variations of soil properties, the different crops and cultivation manner, microbial features (microbial biomass carbon and population density) of natural Pellic Vertisols predominately varied in depth but followed the typical for native soils trend of decreasing amounts down the profiles. In both soils, heterotrophic, oligotrophic and oligonitrophilic bacteria were the most numerous groups but in the deepest horizons only oligotrophs dominated. The oligotroph-pedoturbation observed in A’”ΠΊ and ACk horizons as an atypical population decline is a specific feature of studied Smolnitsas. Due to the high spatial variation of oligonitrophilic bacteria density this group could be used as bioindicator of soil anthropogenization including pyrogenic carbon (PyC) accumulation. Data suggests that additional inputs of PyC in soils surrounding coalfield could decouple SOM and PyC, supress microbiome synergy and dependency on PyC. Only some nutrients (organic carbon, phosphorus, potassium and easily mobile humic and fulvic acids) determined the microbial growth and density in studied soils while soil moisture, depth, carbonates and clay contents were not significant factors. Available nitrogen positively influenced microbiome status only in control soil with exception of oligotrophs for which soil pH was determinative. PH is not a microbial determinant in natural soils beyond the mentioned exception.

Keywords: Pellic Vertisols; microbial biomass; microbial density; pyrogenic carbon; soil nutrients

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