The paper examines the regularities of the post-agrogenic evolution of soils of differing age in the Herakleian Peninsula (southwestern Crimea, Ukraine), which developed under conditions of the sub-Mediterranean climate and have been cultivated since ancient times. Whether developed under steppe or sub-Mediterranean forest vegetation, the Crimean cinnamonic soils display different physico-chemical and geochemical characteristics after 1600 years under no cultivation. It is demonstrated that among 40 examined physico-chemical and geochemical soil characteristics, only ten are sufficiently informative to diagnose the post-agrogenic regime of a soil system. In the geographic and pedogenetic grouping of post-antique long-fallow soils, labile phosphorus content and the hue of soil colour prove to be of primary importance.
Rendzic Leptosols are intrazonal soils formed on limestone bedrock. The specialty of these soils is that parent rock material is more influential in shaping soil characteristics than zonal factors such as climate, especially during soil formation. Unlike fast evolving Podzols due to their leaching regime, Leptosols do not undergo rapid development due to the nature of the limestone. Little is known how microbiome reflects this process, so we assessed microbiome composition of Rendzic Leptosols of different ages, arising from disruption and subsequent reclamation. The mountains and foothills that cover much of the Crimean Peninsula are ideal for this type of study, as the soils were formed on limestone and have been subjected to anthropogenic impacts through much of human history. Microbiomes of four soil sites forming a chronosequence, including different soil horizons, were studied using sequencing of 16S rRNA gene libraries and quantitative PCR. Dominant phyla for all soil sites were Actinobacteria, Proteobacteria, Acidobacteria, Bacteroidetes, Thaumarchaeota, Planctomycetes, Verrucomicrobia and Firmicutes. Alpha diversity was similar across sites and tended to be higher in topsoil. Beta diversity showed that microbiomes diverged according to the soil site and the soil horizon. The oldest and the youngest soils had the most similar microbiomes, which could have been caused by their geographic proximity. Oligotrophic bacteria from Chitinophagaceae, Blastocatellaceae and Rubrobacteriaceae dominated the microbiome of these soils. The microbiome of 700-year old soil was the most diverse. This soil was from the only study location with topsoil formed by plant litter, which provided additional nutrients and could have been the driving force of this differentiation. Consistent with this assumption, this soil was abundant in copiotrophic bacteria from Proteobacteria and Actinobacteria phyla. The microbiome of 50-year old Leptosol was more similar to the microbiome of benchmark soil than the microbiome of 700-year old soil, especially by weighted metrics. CCA analysis, in combination with PERMANOVA, linked differences in microbiomes to the joint change of all soil chemical parameters between soil horizons. Local factors, such as parent material and plant litter, more strongly influenced the microbiome composition in Rendzic Leptosols than soil age.
The development of the extractive industry leads to the increase in the number of quarries on the territory of the Crimean peninsula and, as a consequence, to the increase of the area occupied by the disturbed lands requiring recultivation. The reclamation of such land plots on the basis of creating the necessary conditions for the development of regenerative successions of zonal vegetation on them and ultimately the formation of soils is much cheaper for land users. Therefore, studies of the rates of soil formation, including using the methods of mathematical modeling of the processes of formation of the humus horizon of the soil over time, have become relevant. Calculation of the economic efficiency of reclamation of the disturbed lands has been carried out for the Alexandrovskoye saw- limestone field in the Chernomorsky region of the Republic of Crimea. The assessment has been carried out within the framework of two models: mining engineering with further self-overgrowing of the reclaimed land plots under pastures and integrational, including both mining engineering and biological stages with possible carrying out a number of agrotechnical works on further improvement of pastures, based on the calculation of the cost-effectiveness indicator. This indicator is based on the selection of the best options for remediation work at the minimum value of the integral operational and investment costs and takes into account the effect of the time factor. The calculation results have shown that, in terms of cost-effectiveness, it is more rational to use the mining engineering model with further self-overgrowing of the sites to be reclaimed when it comes to the reclaiming of the disturbed lands of the Alexandrovskoye quarry.
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