The structure of bacterial communities along two vertical profiles of a deep colluvial soil

The redistribution of soil and associated organic matter across landscape represents a major perturbation to the carbon cycle because the established colluvial soils change the levels of C mineralization and sequestration. In this study, two profiles of a colluvial soil 4 m deep were analyzed to test whether its two layers produced by erosion differ from the organic layer of the original soil and if the microbial characteristics correspond to the soil properties. The structure of microbial communities was assessed by both quantitative PCR and Illumina amplicon sequencing. Microbial activities were determined by hydrolytical enzymes. The bacterial community structure was correlated with vertical gradients of soil chemical properties. The dominating bacterial phyla were the same along the whole profile but their relative abundance changed. The upper horizon determined by tillage and reaching to approx. 75 cm had highest values of dissolved organic carbon, P and K and was characterized by Proteobacteria and Bacteroidetes. Also, the activities of hydrolytical enzymes occurred mostly there. The second horizon of deposited soil reaching to approx. 250 cm was characterized by Acidobacteria and Gemmatimonadetes. The lowest horizon of buried Chernozem was characterized by increased soil organic carbon, manganese, iron and sulfate and characterized by Nitrospirae and Rubrobacteria. The community analysis indicated that chemolithotrophic processes might be important in these buried horizons so the decomposition may be slower and residence times for these deep carbon pools longer than in the original upper horizons. In these colluvial systems, erosion could lead to soil organic C stabilization.