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The effect of arable soil was quantified against non-cultivated soil on easily degradable carbon and other selected microbiological factors, i.e. soil microbial biomass, respiration activity, and dehydrogenase activity. The intent was to ascertain whether easily degradable carbo can be useful as a sensitive indicator of both soil biological degradation and microbial hotspots indication. As a result, it was found that soil respiration activity was significantly higher (p <0.0001) in all controls, ranging between 30-60 vs. 11.5-23.7 µmol CO2 kg d.m.-1 h-1 for the arable soils. Dehydrogenase activity was significantly lower in the arable soil (down to 35-40% of the control values, p <0.001) varying depending on the soil type. The microbial biomass was also significantly higher at the non-cultivated soil (512-2807 vs. 416-1429 µg g-1 d.m., p <0.001), while easily degradable carbon ranged between 620-1209 mg kg-1 non-cultivated soil and 497-877 mg kg-1 arable soil (p <0.0001). It was demonstrated that agricultural practices affected soil properties by significantly reducing the levels of the studied parameters in relation to the control soils. The significant correlations of easily degradable carbon-respiration activity (ρ = 0.77*), easily degradable carbon-dehydrogenase activity (ρ = 0.42*), and easily degradable carbon-microbial biomass (ρ = 0.53*) reveal that easily degradable carbon is a novel, suitable factor indicative of soil biological degradation. It, therefore, could be used for evaluating the degree of soil degradation and for choosing a proper management procedure. [ABSTRACT FROM AUTHOR]

The aim of the study was to demonstrate the impact of soil agricultural usage on the abundance of ammonifying bacteria (AB) and their activity, expressed as arginine ammonification (AA). Five agriculturally exploited types of soils (FAO): Haplic Luvisol, Brunic Arenosol, Mollic Gleysol, Eutric Fluvisol, and Rendzina Leptosol were studied. The controls were non-agricultural soils of the same type located in close proximity to agricultural sites. The tested soils varied in terms of pH (4.18-7.08), total carbon (8.39-34.90 g kg), easily degradable carbon content (0.46-1.11 g kg), moisture (5.20-13.50 %), and nitrogen forms (mg kg): 1.68-27.17, 0.036-0.862, 0.012-3.389 for nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen, respectively. The AB abundance in agricultural soils ranged from 1.1 to 6.4 × 10 cfu g, while in the controls it was significantly higher-from 2.0 to 110 × 10 cfu g of soil. Also, AA in the controls was three-times higher than in the agricultural soils. Strong associations between AA and the abundance of AB in the control (r = 0.954***) and agricultural soils (r = 0.833***) were proved. In the agricultural soils, the AB abundance and AA were influenced by pH (r = 0.746*** and r = 0.520***) and carbon content (r = 0.488*** and r = 0.391***). The AB abundance was also affected by easily degradable carbon (r = 0.517**) and nitrite nitrogen (r = 0.376*), whilst ammonium nitrogen influenced AA (r = 0.451*). Our results indicate that the abundance of AB and AA may be good indicators of soil biological conditions. [ABSTRACT FROM AUTHOR]

The main goal of the study was to determine new metagenomic indicators demonstrating sensitivity to soil fatigue as an effect of long-term agricultural use as well as new metagenomic indicators demonstrating bacterial resistance to human agricultural activity. Thirty-one soil samples (agriculturally exploited soil and wastelands – serving as controls) were taken for the study, in the south-eastern part of Poland. For determination of biodiversity, next generation sequencing of the 16S rRNA metagenomic amplicons were used with the Ion Torrent™ technology. Bacterial sequences were clustered into operational taxonomic units (OTUs) based on a 99% similarity threshold. The correlation matrix was constructed to assess the relationships between bacterial families and genera and the environmental data. In the studied soils, 118 families and 305 genera were identified. Among them, 10 families were recommended as sensitive indicators of soil fatigue: Sphingomonadaceae  >  Chitinophagaceae  >  Flavobacteriaceae  >  Oxalobacteraceae  >  Acetobacteraceae  >  Myxococcaceae  >  Comamonadaceae  >  Pseudomonadaceae  >  Burkholderiaceae  >  Rhodanobacteraceae . Analogically, 8 bacterial genera sensitive to agricultural practices were found: Pelomonas  >  Ramlibacter  >  Flavobacterium  >  Rhizobacter  >  Steroidobacter  >  Cellvibrio  >  Halliangium  >  Pseudomonas . Their sensitivity was confirmed by a decrease in the number of OTUs in the agricultural soils, in comparison to the wastelands. In contrast, 5 bacterial genera that should be considered as indicators of resistance to agricultural land use were proposed: Nitrosospira  >  Rhodanobacter  >  Aquicella  >  Burkholderia  >  Mucilaginibacter . Statistical tests demonstrated that the most important factors for the abundances of bacterial families and genera included soil acidity (pH), easily degradable carbon (EDC), total carbon (TC), nitrite nitrogen (N-NO 2 ), magnesium (Mg) and calcium (Ca) content, and soil moisture. [ABSTRACT FROM AUTHOR]