Soil bacteria communities under slash and burn in mozambique as revealed by metataxonomic approach

The “slash and burn” system is a subsistence agronomical practice widely spread in tropical areas all over the world. This system has been deeply studied, especially for its impacts on agronomical aspects and soil physicochemical properties, while the knowledge on their microbial diversity is scarce. In the present study, for the first time the soil bacterial diversity of three locations from central Mozambique where “slash and burn” has been practiced with different duration of the forest fallow period (≈25, 35, and ≈50 years) has been elucidated through a metataxonomic approach. Bacterial communities were evaluated on genetic horizons of soils under charcoal kiln, crop field, and forest. The aim of this study was to examine the influence of spatial (location and land use), temporal (forest fallow period), and vertical (horizons) variations in selecting bacterial populations in relation to the physico-chemical properties of the soil. Metataxonomic analysis detected 25 different phyla whose distribution varied horizontally and vertically in relation to soil properties: pH, easily oxidizable organic carbon, total nitrogen, and available phosphorous, but also particle-size distribution and mineralogical composition. Such properties were strongly affected and altered by land use management; in particular, charcoal kilns showed better soil properties and the greatest differences in microbial community with respect to crop field and forest, 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 microbial community. The uncommon application of the pedologic approach for microbial evaluation has allowed detecting a clear separation in microbiota composition along the soil profile, with eutrophic bacteria mainly located in the A horizons, while oligotrophic bacteria abounded in the Bo horizons. Considering horizontal and vertical heterogeneity in the same study represent a novelty for bacteria metataxonomic analysis.