Effects of vegetation and seasonality on bacterial communities in Amazonian dark earth and adjacent soils

Amazonian Dark Earth (ADE) in the Brazilian Amazon is the main evidence left by pre-Columbian indigenous populations indicating that infertile soils can be transformed into highly fertile ground. Changes in vegetation cover and seasonality are likely to influence microbial communities; however, little is known about these effects on ADE. Therefore, this study compared the effects of two land use systems in ADE and adjacent soil (ADJ) during the rainy and dry seasons using biochemical and molecular tools. Bacterial community function was determined by community level physiological profile (CLPP), bacterial community structure by terminal restriction length polymorphism (T-RFLP), and bacterial community composition by pyrosequencing of the V4 16S rRNA gene region. Our results show that the community structure is highly affected by vegetation, in both, ADE and ADJ soils. Regarding community function, Average Well Color Development (from Biolog substrates) were higher in ADE than ADJ during the rainy season and kept the same pattern of substrate utilization during the dry season and finally, community composition showed to be influenced even at the level of family, mostly by soil type rather than vegetation. Collectively, our study provides insights into processes affecting the bacterial community assemblages in both, ADE and adjacent soils. Key words: Amazonian soils, vegetation type, seasonality, soil bacteria.