No abstract

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.

Composting has been recognised an alternative method to tannery sludge recycling and afterwards to be used in agriculture. As the tannery sludge contains salts and chromium, the application of composted tannery sludge (CTS) should be performed carefully to minimise negative effects on soil microbial properties. Therefore, this study evaluated the effects of 5-year repeated CTS amendment on soil microbial biomass (SMB) and enzyme activities in a tropical soil. CTS was applied during 5 years at 0, 2.5, 5, 10 and 20 Mg ha(-1), and at the fifth year, the microbial biomass C (MBC) and N (MBN), basal and substrate-induced respiration (SIR), metabolic quotient (qCO₂) and dehydrogenase (DHA) and fluorescein diacetate (FDA) hydrolysis were determined in the soil samples. Soil MBC and MBN showed the highest values with the amendment of 5 Mg ha(-1) CTS. Soil respiration increased with the increase in CTS rates, while SIR showed the highest values with the amendment of 0, 2.5 and 5 Mg ha(-1) CTS. DHA activity showed the highest values with the amendment up to 2.5 Mg ha(-1), while FDA hydrolysis increased up to the rate of 5 Mg ha(-1) CTS. The results show that after 5 years of permanent amendment of CTS, soils amended with 2.5 Mg ha(-1) have SMB and enzymatic activities similar to those in unamended soil.

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.

Agroforestry systems (AFS) are considered alternative land use options to help prevent soil degradation and improve soil microbial biomass and organic C status. However, it is unclear how different densities of babassu palm [Attalea speciosa (syn. Orbignya phalerata)], which is an important tree in Northeast Brazil, affect the soil microbial biomass. We investigated the soil microbial biomass C and activity under AFS with different densities of babassu palm associated with Brachiaria brizantha grass. Soil microbial biomass C (MBC), soil microbial biomass N (MBN), MBC:total organic C ratio, fluorescein diacetate hydrolysis and dehydrogenase activity showed highest values in plots with high density of babassu palm. On the other hand, the respiratory quotient (qCO 2 ) was significantly greater in plots without babassu palm. Brachiaria brizantha in monoculture may promote C losses from the soil, but AFS with high density of babassu palm may increase the potential of soils to accumulate C. ResumenLos sistemas agroforestales (AFS, por sus siglas en inglés) son opciones alternativas de uso de la tierra que ayudan a prevenir la degradación del suelo y mejorar la biomasa microbiana y el estado del carbono (C) orgánico. Babasú [Attalea speciosa (syn. Orbignya phalerata)] es una importante palma nativa que forma bosques en los estados Maranhão y Piauí, nordeste de Brasil; no obstante no se conoce su efecto sobre la biomasa microbiana del suelo cuando crece en diferentes densidades. En el estudio se evaluaron los efectos sobre el C y la actividad de la biomasa microbiana del suelo en AFS con 3 densidades de babasú en pasturas de Brachiaria brizantha. El C y el nitrógeno de la biomasa microbiana (MBC resp. MBN) del suelo, la relación de MBC:C orgánico total del suelo, la hidrólisis de diacetato de fluoresceína y la actividad de la deshidrogenasa mostraron valores más altos en las parcelas con alta densidad de babasú. Por otra parte, el cociente respiratorio (qCO2) fue significativamente mayor en las parcelas sin babasú. El pasto B. brizantha en monocultivo puede promover la pérdida de C del suelo, pero los AFS con alta densidad de la palma pueden aumentar el potencial de los suelos para acumular C.