Land use intensification in the humid tropics increased both alpha and beta diversity of soil bacteria

Anthropogenic pressures on tropical forests are rapidly intensifying, but our understanding of their implications for biological diversity is still very limited, especially with regard to soil biota, and in particular soil bacterial communities. Here we evaluated bacterial community composition and diversity across a gradient of land use intensity in the eastern Amazon from undisturbed primary forest, through primary forests varyingly disturbed by fire, regenerating secondary forest, pasture, and mechanized agriculture. Soil bacteria were assessed by paired-end Illumina sequencing of 16S rRNA gene fragments (V4 region). The resulting sequences were clustered into operational taxonomic units (OTU) at a 97% similarity threshold. Land use intensification increased the observed bacterial diversity (both OTU richness and community heterogeneity across space) and this effect was strongly associated with changes in soil pH. Moreover, land use intensification and subsequent changes in soil fertility, especially pH, altered the bacterial community composition, with pastures and areas of mechanized agriculture displaying the most contrasting communities in relation to undisturbed primary forest. Together, these results indicate that tropical forest conversion impacts soil bacteria not through loss of diversity, as previously thought, but mainly by imposing marked shifts on bacterial community composition, with unknown yet potentially important implications for ecological functions and services performed by these communities

A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network

Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazonia Sustentavel, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.Keywords: Social–ecological systems, Tropical forests, Land use, Interdisciplinary research, Sustainability, Trade-off

The culture medium volume and the inoculation method should be considered in semi-quantitative screening of calcium phosphate solubilization by bacteria

Agar media with insoluble phosphates are used for semi-quantitative screening of phosphate-solubilizing bacteria based on the solubilization halo formed around the colonies. We show that the volume of the culture medium (15, 20, and 30 mL) and the inoculation method (toothpick vs microdrop) strongly influence the diameter of the solubilization halo, and this should be considered in advance selection of the isolates most efficient in this process

Ecotoxic effects of the vehicle solvent dimethyl sulfoxide on Raphidocelis subcapitata, Daphnia magna and Brachionus calyciflorus

International audienceDimethyl sulfoxide (DMSO) is widely used as a vehicle solvent inecotoxicity bioassays.Despite its frequent use, it could be toxic fororganisms at some concentrations. Hence, this study aims toinvestigate the effects of DMSO on the modelorganisms: microalgae Raphidocelis subcapitata, microcrustaceanDaphnia magna, and rotifer Brachionus calyciflorus. DMSO wasapplied to the organisms in concentrations ranging from 0.031%to 4%. For R. subcapitata the lowest observed effectconcentration (LOEC) after 72 h of exposure was 0.125% DMSO.The 50% effective concentration (EC50) was 2.138 ± 0.372%. InD. magna, significant differences in the mobility after 24 h or 48 hof exposure were observed for 1% DMSO being 1.712 ± 0.207%and 1.167 ± 0.220% DMSO the EC50 observed for 24 h and 48 hexposure, respectively. For B. calyciflorus, it was not possible tovalidate the tests performed, as there were insufficient animalsalive in the control conditions at the end of the exposure period.Therefore, we recommended avoiding DMSO as a vehicle inassays using B. calyciflorus, and to use final DMSO concentrationsin an experimental solution not exceeding 0.125% forR. subcapitata and 0.5% for D. magna. Finally, using a maximumof 0.01% DMSO is safe for the organisms tested.The effects of the vehicle solvent dimethyl sulfoxide (DMSO)were investigated in three aquatic model organisms, themicroalgae Raphidocelis subcapitata, the microcrustacean Daphniamagna and the rotifer Brachionus calyciflorus. As a result, negativeeffects on growth rate for the algae population, immobilisation ofdaphnids and inhibition of rotifer reproduction was observedobtaining EC50 close to 1% of DMSO for all these cases

Agronomic and environmental implications of using a By-Product of the Intermediate Tanning Processes as Nitrogen Fertilizer

Nitrogen (N) is an important nutrient for agriculture, and Brazil is heavily dependent on N imports. A by-product of the intermediate processes of tanning (BPIPT) may be used as an N fertilizer which will reduce this dependency, but its chromium (Cr) content is a matter of concern. This work assessed Cr (III, VI) and N (total, inorganic) contents in four soil samples with contrasting characteristics (especially with respect to their content of manganese (Mn), a potential Cr(III) oxidant), following the addition of the BPIPT. Chemical and microbiological indicators of soil quality were measured to assess the agronomic and environmental implications of the BPIPT addition in Brazilian soils. Our results indicate that the BPIPT is a promising source of N. The originally available Mn content in the soil did not influence the effect of the BPIPT on soil Cr(VI) content. Finally, microbial activity was generally stimulated after BPIPT addition to the soil. This information is relevant because: 1) it shows that the beneficial use of the BPIPT as an N fertilizer is important for adding value to a by-product with agronomic potential; and 2) it indicates that, at the dosage of the BPIPT used in this study (2.5 g kgsoil−1), the typical increases in the soil concentration of labile Cr (0–25 mg kgsoil−1) and Cr(VI) (0–0.8 mg kgsoil−1) due to the application of the BPIPT are not detrimental to biological activity in the soil. However, further investigations are still necessary to evaluate the mobility of these Cr species in the soil and possible risks of groundwater contamination, which were not addressed in this study

Bactérias diazotróficas em solos sob seringueira

Diversos relatos evidenciam os benefícios de procariotos fixadores de nitrogênio atmosférico no crescimento e na nutrição de muitas espécies vegetais; entretanto, não há, até o momento, nenhum trabalho visando à prospecção desses microrganismos na rizosfera da seringueira (Hevea brasiliensis). Assim, os objetivos deste trabalho foram verificar a ocorrência de bactérias diazotróficas em solos sob plantio de seringueira, assim como em suas raízes, e isolar e caracterizar essas bactérias. Para essa finalidade, coletaram-se amostras de solo e de raízes finas de seringueiras cultivadas no Campus Experimental da Universidade Federal de Lavras (Lavras, MG) para inoculação em meios de cultura semissólidos sem N na forma combinada, de modo a favorecer o crescimento de algumas espécies de bactérias diazotróficas. Foram obtidos 19 isolados nas amostras de solo, e não houve crescimento de bactérias fixadoras de nitrogênio nas culturas com amostras de raízes. A caracterização celular e das colônias desses isolados indicou que 17 deles produzem grande quantidade de exopolissacarídeo elástico, algumas vezes cartilaginoso. Eles são todos Gram-negativos, com formato celular de bastonete, imóveis e com dois glóbulos de poli-β-hidroxibutirato (PBH), um em cada extremidade do bastonete. O sequenciamento do 16S rDNA e sua análise filogenética confirmaram que isolados representativos desse grupo pertencem ao gênero Beijerinckia (B. indica e B. derxii) e que os outros dois isolados Gram-positivos pertencem ao gênero Bacillus. A presença da nitrogenase - a enzima responsável pela fixação biológica do nitrogênio atmosférico (FBN) - foi confirmada por meio da técnica de redução do acetileno. Conclui-se que, no solo sob plantio de seringueira, houve predominância de diazotróficas de vida livre pertencentes ao gênero Beijerinckia (B. indica e B. derxii), não havendo indícios de bactérias endofiticas ou rizosféricas

Bradyrhizobium campsiandraesp. nov., a nitrogen-fixing bacterial strain isolated from a native leguminous tree from the Amazon adapted to flooded conditions

The nitrogen-fixing bacterial strain UFLA 01-1174(T)was isolated from nodules ofCampsiandra laurilifoliaBenth. originating from the Amazon region, Brazil. Its taxonomic position was defined using a polyphasic approach. Analysis of the 16S rRNA gene placed the strain in theBradyrhizobiumgenus, the closest species beingB. guangdongenseCCBAU 51649(T)andB. guangzhouenseCCBAU 51670(T), both with 99.8% similarity. Multilocus sequence analysis (MLSA) ofrecA,gyrB,glnII,rpoB,atpD, anddnaKindicated that UFLA 01-1174(T )is a new species, most closely related toB. stylosanthisBR 446(T)(94.4%) andB. manausenseBR 3351(T)(93.7%). Average nucleotide identity (ANI) differentiated UFLA 01-1174(T)from the closest species with values lower than 90%. The G + C content in the DNA of UFLA 01-1174(T )is 63.6 mol%. Based on this data, we conclude that the strain represents a new species. The name proposed isBradyrhizobium campsiandrae, with UFLA 01-1174(T)(= INPA 394B(T) = LMG 10099(T)) as type strain