The Cerrado biome in the Sete Cidades National Park, an Ecological Reserve in Northeastern Brazil, has conserved its native biodiversity and presents a variety of plants found in other savannas in Brazil. Despite this finding the soil microbial diversity and community structure are poorly understood. Therefore, we described soil bacterial diversity and distribution along a savanna vegetation gradient taking into account the prevailing environmental factors. The bacterial composition was retrieved by sequencing a fragment of the 16S ribosomal RNA gene. The bacterial operational taxonomic units (OTUs) were assigned to 37 different phyla, 96 classes, and 83 genera. At the phylum level, a core comprised by Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, Verrucomicrobia and Planctomycetes, was detected in all areas of Cerrado. 'Cerrado stricto sensu' and 'Cerradao' share more similarities between edaphic properties and vegetation and also present more similar bacterial communities, while 'Floresta decidual' and 'Campo graminoide' show the largest environmental differences and also more distinct bacterial communities. Proteobacteria (26%), Acidobacteria (21%) and Actinobacteria (21%) were the most abundant phyla within the four areas. All the samples present similar bacteria richness (alpha diversity) and the observed differences among them (beta diversity) were more related to the abundance of specific taxon OTUs compared to their presence or absence. Total organic C, N and P are the main abiotic factors structuring the bacterial communities. In summary, our findings show the bacterial community structure was clearly different across the Cerrado gradient, but that these environments share a bacterial phylum-core comprising Proteobacteria, Acidobacteria, Actinobacteria, Verrucomicrobia and Planctomycetes with other Brazilian savannas.

The intensive use of soil for pasture establishment has promoted land degradation. However, well-managed pasture systems may contribute to the improvement of the soil biological properties. The aim of this study was to evaluate the soil microbial biomass, enzymes activity, and catabolic diversity under six different pastures: Andropogon gayanus, Brachiaria brizantha, Panicum maximum, Cynodon dactilon, agroforestry system, and native vegetation. Soil microbial biomass was estimated by the fumigation-extraction method, while enzyme activity was determined through substrate use. The catabolic diversity was evaluated by the community-level physiological profiling method. Microbial biomass C was higher in the soils under the agroforestry system and native vegetation, whereas microbial biomass N was higher in the soil under Brachiaria. Acid phosphatase activity and fluorescein diacetate hydrolysis were higher in agroforestry system and native vegetation, respectively. Dehydrogenase activity was higher in the soil under Brachiaria and Cynodon. Richness and diversity of community-level physiological profiling were higher in the soils under the agroforestry system and native vegetation. The highest numbers of C sources metabolized by microorganisms were found in the agroforestry system and native vegetation. This study showed that soil microbial community from pasture systems subjected to different management showed different biomass, activity, and catabolic diversity.

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The different physiognomies and soil conditions across the Cerrado gradient may influence soil microbial biomass. The present study evaluated the soil microbial biomass and enzyme activity across a preserved Cerrado gradient and correlated these with environmental conditions. The site, sampling period and their interaction influenced soil microbial biomass and activity. Soil conditions, i.e., chemical and microclimatic properties, varied across the Cerrado gradient and influenced soil microbial biomass and activity. The highest and lowest values for microbial biomass and enzyme activity were found in Cerradao and Campo graminoide, respectively, during both seasons. Multivariate analysis showed that the sites were clearly separated into different groups, indicating that distinct physiognomies and environmental conditions influenced soil microbial biomass and enzyme activities.

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