Contrasting Soils in Organic Carbon Reflect Distinction in Soil Bacterial Community Composition.

The soil organic carbon (SOC) is crucial to maintain and improve many ecosystem services provided by soils. Chilean soils derived from volcanic material (Andisols) have a high SOC content, reaching values up to 12%. These soils enclose important agroecosystems as a result of their high natural fertility and physical properties (low bulk density, high available water and aggregate stability). The goal of this study was to determine the bacterial structure and composition in soils with high organic carbon Andisols (8-11%) compared with lower organic carbon Inceptisols (1-3%). We characterized the bacterial communities by 16S rRNA gene sequencing (Illumina) in natural and cropland systems under the same climate conditions at 10 cm depth. Our results showed no variation in soil bacterial richness or diversity as SOC increased. However, differences were observed in bacterial composition between the types soils studied. The common core of operational taxonomic units (OTUs) was represented by less than 0.5% over the total OTUs. Regarding common core taxonomy, phyla Acidobacteria (28%), Proteobacteria (26%) and Actinobacteria (14%) were dominant. Interestingly, major differences between soils were found within the most abundant OTUs (>1%) that represent 10% approximately of the total bacterial community. Among dominant OTUs, phyla WD272, Firmicutes and Planctomycetes were only observed in Inceptisols. Minority and rare OTUs (90% of the total community) showed less differences at taxonomic level. Our results provide additional insights into how soil bacterial communities may relate to SOC content, becoming potential indicators of soil quality for improving carbon restoration and conservation practices.