CHANGES IN THE SOIL MICROBIOME OF A MILITARY TRAINING GROUND

Abstract

An analysis of the heavy metal content in the soil samples taken from the military training ground revealed that the maximum permissible concentrations for Cu, Cr, and Zn had been exceeded. The levels of other metals in the soils studied were within acceptable limits. As a result of the ammunition explosions, metals such as Cu, Cr, Hg, and Se were released into the soil, as the concentration of these metals in the sample taken from the craters was statistically higher than in the soil sample taken from areas without visible signs of damage. In particular, copper levels increased 2.4-fold (p<0.001), chromium levels 8.3-fold (p<0.001), mercury levels 4.0-fold (p=0.015), and selenium levels 2.1-fold (p=0.001). No statistically significant differences in the content of other metals were found between the samples. Among the 10 most abundant families identified in the metagenome of the soils sampled from the military training ground, the relative abundance of Mycobacteriaceae was 3.06 times higher in soil samples from craters (ranging from 0.81% in a sample of undamaged soil to 2.49% in soil from a crater). An increase was also observed in the proportion of sequences identified as belonging to the families Xanthobacteraceae (1.87- fold), Micrococcaceae (1.13-fold) and Solirubrobacteraceae (1.08-fold). In contrast, a sharp decline was observed in the relative abundance of the Nitrososphaeraceae family, whose proportion in the crater sample decreased by 18.23-fold (from 3.48% to 0.19%). In addition, there was a decrease in the proportion of families such as 67-14 (2.38-fold), Gemmatimonadaceae (1.72-fold), Nocardioidaceae (1.45-fold), Streptomycetaceae (1.4-fold) and Pseudomonadaceae (1.29-fold). Among the 10 most abundant genera identified in the metagenome of the studied soils, the relative abundance of sequences identified as members of the genus Candidatus Solibacter was 3.23 times higher (from 0.46% in a soil sample without visible damage to 1.50% in a soil sample from a crater), and Mycobacterium was 3.06 times higher (from 0.82% to 2.49%, respectively). The proportion of sequences belonging to the genera Bradyrhizobium (2.60 times higher) and Candidatus Udaeobacter (2.25 times higher) was also greater. In contrast, the sample from the crater showed a decline in the relative abundance of several taxa, particularly the genus RB41, whose proportion decreased 3.29-fold (from 1.87% to 0.57%). In addition, there was a decrease in the relative abundance of genera such as Pseudonocardia (2.45-fold), Gaiella (2.28-fold), Streptomyces (1.75-fold), Nocardioides (1.51-fold), and Pseudomonas (1.29-fold).