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Soybean cultivation in tropical regions relies on symbioses with nitrogen-fixing Bradyrhizobium and plant growth-promoting bacteria (PGPBs), reducing environmental impacts of N fertilizers and pesticides. We evaluate the effects of soybean inoculation with different bacterial consortia combined with PGPBs or microbial secondary metabolites (MSMs) on rhizosoil chemistry, plant physiology, plant nutrition, grain yield, and rhizosphere microbial functions under field conditions over three growing seasons with four treatments: standard inoculation of Bradyrhizobium japonicum and Bradyrhizobium diazoefficiens consortium (SI); SI plus foliar spraying with Bacillus subtilis (SI + Bs); SI plus foliar spraying with Azospirillum brasilense (SI + Az); and SI plus seed application of MSMs enriched in lipo-chitooligosaccharides extracted from B. diazoefficiens and Rhizobium tropici (SI + MSM). Rhizosphere microbial composition, diversity, and function was assessed by metagenomics. The relationships between rhizosoil chemistry, plant nutrition, grain yield, and the abundance of microbial taxa and functions were determined by generalized joint attribute modeling. The bacterial consortia had the most significant impact on rhizosphere soil fertility, which in turn affected the bacterial community, plant physiology, nutrient availability, and production. Cluster analysis identified microbial groups and functions correlated with shifts in rhizosoil chemistry and plant nutrition. Bacterial consortia positively modulated specific genera and functional pathways involved in biosynthesis of plant secondary metabolites, amino acids, lipopolysaccharides, photosynthesis, bacterial secretion systems, and sulfur metabolism. The effects of the bacterial consortia on the soybean holobiont, particularly the rhizomicrobiome and rhizosoil fertility, highlight the importance of selecting appropriate consortia for desired outcomes. These findings have implications for microbial-based agricultural practices that enhance crop productivity, quality, and sustainability.

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The ruderal babassu palm (Attalea speciosa) is expanding on large areas of degraded Amazon landscapes. Decomposition of leaves and roots is in the center of plant:soil interactions. We evaluated decomposition and nutrient concentrations of leaves and fine roots of babassu in comparison with two exotic reference species, Acacia mangium (slow degradability) and Leucaena leucocephala (fast degradability), in a 138-day litterbag assay carried out in secondary forest stands of different age and babassu abundance. We chose 4-mm over 2-mm mesh litterbags based on a pilot study. Babassu leaves degraded slower than leaves of A. mangium and L. leucocephala, and also had lower nitrogen, phosphorus and calcium concentrations in all stages of decomposition. By contrast, potassium concentrations in babassu leaves were higher than in both reference species at 0 and 50 days. Roots of all three species decomposed slower than leaves. Compared to the leaves, both biomass loss and nutrient concentrations differed less between babassu and reference-species roots, except for lower nitrogen concentration in babassu roots. Leaf-litter decomposition of all three species was significantly faster in old than in young secondary forest, suggesting an acceleration of decomposition along succession. Babassu leaves decomposed faster in old babassu-dominated than non-dominated secondary forest, pointing to the existence of specialized decomposer communities in babassu-dominated stands. (AU)

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Grasses of the Urochloa genus have been widely used in crop-livestock integration systems or as cover crops in no-till systems such as in rotation with maize. Some species of Urochloa have mechanisms to reduce nitrification. However, the responses of microbial functions in crop-rotation systems with grasses and its consequence on soil N dynamics are not well-understood. In this study, the soil nitrification potential and the abundance of ammonifying microorganisms, total bacteria and total archaea (16S rRNA gene), nitrogen-fixing bacteria (NFB, nifH), ammonia-oxidizing bacteria (AOB, amoA) and archaea (AOA, amoA) were assessed in soil cultivated with ruzigrass (Urochloa ruziziensis), palisade grass (Urochloa brizantha) and Guinea grass (Panicum maximum). The abundance of ammonifying microorganisms was not affected by ruzigrass. Ruzigrass increased the soil nitrification potential compared with palisade and Guinea grass. Ruzigrass increased the abundance of N-fixing microorganisms at the middle and late growth stages. The abundances of nitrifying microorganisms and N-fixers in soil were positively correlated with the soil N-NH4+ content. Thus, biological nitrogen fixation might be an important input of N in systems of rotational production of maize with forage grasses. The abundance of microorganisms related to ammonification, nitrification and nitrogen fixing and ammonia-oxidizing archea was related to the development stage of the forage grass.

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RESUMO

The ruderal babassu palm (Attalea speciosa) is expanding on large areas of degraded Amazon landscapes. Decomposition of leaves and roots is in the center of plant:soil interactions. We evaluated decomposition and nutrient concentrations of leaves and fine roots of babassu in comparison with two exotic reference species, Acacia mangium (slow degradability) and Leucaena leucocephala (fast degradability), in a 138-day litterbag assay carried out in secondary forest stands of different age and babassu abundance. We chose 4-mm over 2-mm mesh litterbags based on a pilot study. Babassu leaves degraded slower than leaves of A. mangium and L. leucocephala, and also had lower nitrogen, phosphorus and calcium concentrations in all stages of decomposition. By contrast, potassium concentrations in babassu leaves were higher than in both reference species at 0 and 50 days. Roots of all three species decomposed slower than leaves. Compared to the leaves, both biomass loss and nutrient concentrations differed less between babassu and reference-species roots, except for lower nitrogen concentration in babassu roots. Leaf-litter decomposition of all three species was significantly faster in old than in young secondary forest, suggesting an acceleration of decomposition along succession. Babassu leaves decomposed faster in old babassu-dominated than non-dominated secondary forest, pointing to the existence of specialized decomposer communities in babassu-dominated stands.(AU)

A palmeira ruderal babaçu (Attalea speciosa) se expande em grandes áreas da Amazônia já desmatada e degradada. A decomposição é chave na dinâmica sucessional e nas interações planta:solo. Avaliamos decomposição e concentração de nutrientes de folhas e raízes finas de babaçu e de duas espécies exóticas de referência, Acacia mangium (decomposição lenta) e Leucaena leucocephala (decomposição rápida), em capoeiras de diferente idade e grau de dominância de babaçu usando litterbags durante 138 dias. Usamos litterbags com malha de 4 mm em vez de 2 mm, com base em um estudo-piloto. As folhas de babaçu se decompuseram mais lentamente que as de A. mangium e L. leucocephala, e apresentaram concentrações mais baixas de nitrogênio, fósforo e cálcio em todos os estágios de decomposição. Em contraste, a concentração de potássio em folhas de babaçu foi mais alta que nas espécies de referência aos 0 e 50 dias. Raízes se decompuseram mais lentamente que folhas nas três espécies. Tanto a perda de massa, como a concentração de nutrientes diferiram menos entre as raízes que entre as folhas de babaçu e as espécies de referência, exceto a concentração de nitrogênio nas raízes de babaçu. A decomposição foliar das três espécies foi significantemente mais rápida em capoeira velha que em capoeira jovem, sugerindo uma aceleração da decomposição ao longo dos estágios sucessionais. A decomposição foliar do babaçu foi mais rápida em capoeira velha com alta dominância de babaçu que em capoeira velha com baixa dominância, apontando para a existência de comunidades especializadas de decompositores em áreas dominadas por babaçu.(AU)

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A cidade de São Luís, capital do estado do Maranhão, possui um sistema ineficiente de tratamento de seus efluentes e boa parte deles é lançada nos rios ou diretamente nas praias. Este trabalho teve como objetivo avaliar o grau de resistência aos metais pesados de 39 cepas de E.coli, isoladas da água de praias da cidade, além de sua suscetibilidade a antibióticos e sua capacidade de produzir biofilme. A análise da resistência aos metais pesados foi realizada pelo método de diluições sucessivas nas concentrações de 1 a 16mM.O teste de sensibilidade, ou antibiograma, foi executado pelo método de difusão em disco, utilizando-se os seguintes antibióticos: Aztreonam, Imipenem, Cefalotina, Ampicilina/Sulbactam, Gentamicina, Ampicilina, Cefuroxima sódica, Amoxicilina, Piperacilina+Tazobactam (TZP), Trimetoprim-Sulfametoxazol (SXT) e Amoxicilina+Ácido Clavulânico (AMC). Para detecção de biofilme nas cepas de E. coli, foram utilizadas as técnicas de Ágar Vermelho Congo (AVC) e Espectrofotometria (ESP). Os resultados mostraram 2 cepas tolerantes a concentrações de Hg a 1mM, 9 cepas resistentes ao Cu e Cd a 4mM e 12 ao Ni a 4mM. O exame de susceptibilidade aos antibióticos mostrou os seguintes percentuais de resistência das amostras: 15 por cento a ATM, 95 por cento a KF, 85 por cento a ASB, 85 por cento a CN, 87 por cento a AMP, 13 por cento a CXM, 5 por cento a TZP, 74 por cento a SXT e 18 por cento a AMC. Quanto à produção de biofilme, 20 por cento apresentaram elevada produção, 36 por cento fraca produção e 44 por cento não produziram. Pela técnica de espectrofotometria, somente 1 cepa (2,5 por cento) revelou-se produtora moderada de biofilme, 5 (12,5 por cento) foram classificadas como não produtoras e as demais, 34 (85 por cento), como fracas produtoras. A presença de bactérias com múltiplos perfis de resistência nas praias de São Luís pode representar riscos para a saúde pública e causar alterações diretas na ecologia das comunidades de micro-organismos marinhos.

The city of São Luís, located in the State of Maranhão has inefficient treatment of sewage, which isreleased into the rivers or directly on the beaches. This study evaluated the resistance of 39 strainsof Escherichia coli to Cu, Ni, Cd and Hg, their susceptibility to antibiotics and ability for biofilmproduction. Samples were collected from the beaches of Ponta D’Areia, São Marcos, Calhau andOlho d’Água. The antibiotic susceptibility tests were performed by the disk diffusion method withthe following antibiotics: Aztreonam (ATM), Imipenem (IMP), Cephalothin (KF), Ampicillin /Sulbactam (ASB), Gentamicin (CN), Ampicillin (AMP), Cefuroxime sodium (CXM), Amoxicillin(AML), Piperacillin Tazobactam (TZP), Trimethoprim-sulfamethoxazole (SXT) and Amoxicillin+ clavulanic acid (AMC). The detection of biofilm production was performed using Congo RedAgar (CRA) and spectrophotometry (ESP). The results showed 2 strains were Hg tolerant (1mM), 9 strains resistant to Cu and Cd (4 mM) and 12 strains resistant to Ni (4 mM). The antibioticsusceptibility tests showed resistance to ATM (15 percent of samples), KF (95 percent), BSA (85 percent), CN (5 percent),AMP (87 percent), CXM (13 percent), TZP (5 percent), SXT (74 percent) and AMC (18 percent). For the synthesis of biofilm inCRA 20 percent showed strong production, 36 percent low and 44 percent did not produce. By spectrophotometryonly 1 (2.5 percent) proved to be a moderate biofilm producer, 5 (12.5 percent) were classified as non-producersand the other 34 (85 percent) weak producers. The presence of bacteria with antimicrobial and heavy metalresistance profiles, and production of biofilms represents a public health risk and cause of directchanges in ecological communities of marine microorganisms.

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