Land-use system shapes soil bacterial communities in Southeastern Amazon region

• Land-use system had a primary effect on the soil bacterial communities.
• Soil chemical parameters such as pH, C, N, NO3− and K are correlated to overall bacterial community.
• Specific phyla are correlated to specific soil chemical parameter.
• Al saturation index, Al, base saturation index, Mg and Ca are correlated with a higher number of individual phyla.

The expansion of the agriculture has become the main agent of disturbance in the Amazon region, and such alteration has consequences on soil microbial communities, which represent the majority of biodiversity in terrestrial ecosystems. In this study we assessed the effects of land-use changes on physicochemical soil properties and, consequently, on the bacterial communities in soils from Southeastern Amazon, Brazil. Soil samples were collected in four distinct land-use systems, i.e. native forest, deforested area, agricultural and pasture fields. The soil bacterial community abundance, structure and composition were addressed using qPCR, one molecular marker (T-RFLP) and high-throughput sequencing of the bacterial 16S rRNA gene, respectively. Obtained data were analyzed using multivariate techniques. We found that the type of land-use had a primary effect on the soil bacterial communities, whereas parameters such as pH, C, N, NO3− and K content significantly correlated to overall community structures. We observed that the abundance and taxonomic diversity of the bacterial 16S rRNA changed to a higher extent according to the land-use system, but they also showed significant temporal turnover within sites. From the total 27 bacterial phyla identified, 12 presented clearly differential distribution across the four land-use systems. Comparison among all sites revealed Acidobacteria and Chlamydiae to be higher abundant in forest soil, Actinobacteria in deforested site, Nitrospira and Deinococcus-Thermus in agriculture and Firmicutes in pasture. When data of specific phyla were correlated to specific soil properties, we demonstrated that parameters such as Al saturation index, Al, base saturation index, Mg and Ca presented correlation with the most number of bacterial groups detected. Thus, we suggest that several soil parameters besides pH should be taken into account when assessing the impacts of land-use change on the microbial communities.