Soil bacterial communities under slash and burn in Mozambique as revealed by a metataxonomic approach

The slash-and-burn system is a subsistence agronomical practice widespread in tropical areas worldwide. This system has been extensively studied, especially for its impacts on agronomical aspects and soil physicochemical properties; however, knowledge of soil microbial diversity under slash and bum is scarce. In this study, for the first time, soil bacterial diversity of three locations from Central Mozambique, where slash and burn has been practiced for different durations of the forest fallow period (ca. 25, 35, and 50 years), was elucidated through a metataxonomic approach. Bacterial communities were evaluated in the genetic horizons of soils under charcoal kilns, crop fields, and forests. The aim of this study was to examine the influence of spatial (location and land use), temporal (forest fallow period), and vertical (horizon) variations on bacterial community structure in relation to soil physicochemical properties. Metataxonomic analysis detected 25 different phyla whose distribution varied horizontally and vertically in relation to soil properties (i.e., pH, easily oxidizable organic carbon, total nitrogen, and available phosphorus), as well as particle size distribution and mineralogical composition. Such properties were strongly affected and altered by land-use management; in particular, charcoal kilns exhibited better soil properties and greater differences in bacterial community than crop fields and forests, which were quite similar. This might suggest the inability of a forest fallow period shorter than 50 years to improve soil fertility and induce changes in bacterial community. The uncommon application of the pedological approach for microbial evaluation facilitated the detection of a clear separation in bacterial composition along the soil profile, with eutrophic bacteria mainly located in the A horizon whereas oligotrophic bacteria were found in the Bo horizon. These horizontal and vertical heterogeneities in the same study represent a novelty for bacterial metataxonomic analysis.