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ABSTRACT Termites can create structures that alter the physical and chemical properties of soils. In this process, termites are selective about the soil constituents they will use to construct their mounds. Considering the common occurrence of termite mounds in Brazilian soils, this study aimed to investigate the selective action of termites in the mound building process. Samples were collected from six termite mounds and control soils (at a distance of 15 to 30 m from the termite mound) in different regions in Brazil to analyze the fine earth fraction. The content of clay fraction, organic C and Fe in pedogenic iron oxides increased in the mounds resulting in specific surface area increments. X-ray diffraction indicated a selectivity of termites by clay-sized particles such as kaolinite, gibbsite and iron oxides (hematite and goethite) rather than larger particles such as quartz. The proportion of low-crystalline iron oxides and the maghemite amount decreased in the mounds. The change of color parameters in the termite mounds was due to a combination of increase in clay fraction, organic carbon and iron oxides. The techniques used were sensitive, indicating changes and similarities between the control soils and the termite mounds.

La selección de rizóbios nativos promisores, fijadores de nitrógeno (N) es importante para la producción de leucaena integrada a pastos para la producción pecuaria. En el estado de Rio Grande do Sul, Brasil (RS) son escasas las informaciones de cepas nativas de rizóbios con capacidad simbiótica con plantas de leucaena. El objetivo de este trabajo fue seleccionar rizóbios nativos, eficientes en la fijación biológica de N en plantas de leucaena en RS. Se tomaron muestras de suelo y nódulos de diferentes locales de RS y luego en el laboratorio se utilizaron semillas de leucena como trampa para capturar los rizóbios. Se realizó un experimento en condiciones de invernadero para evaluar la eficiencia de los rizóbios autenticados como simbiontes de leucaena, siendo determinada la masa seca de la parte aérea (MSPA), masa seca de la raíz, número de nódulos y N acumulado de la parte aérea de la planta (Nac). Los resultados mostraron que los aislados de rizóbios seleccionados Leu01 y Leu02 autenticados como simbiontes de leucaena proporcionaron aumento de la MSPA y Nac en las plantas de leucena, similar al tratamiento no inoculado que recibió fertilización nitrogenada, por lo que podrían ser promisores en futuros estudios en invernadero y campo de esta leguminosa.

As espécies de Adesmia encontradas no Rio Grande do Sul e em Santa Catarina apresentam alta qualidade forrageira e podem ser utilizadas em programas de melhoramento de campos nativos. O objetivo deste trabalho foi avaliar a promoção do crescimento em espécies de adésmia por rizobactérias produtoras de ácido indolacético (AIA). Foram utilizados sete isolados de bactérias de nódulos de adésmia e pertencentes à coleção de rizobactérias da Epagri. Avaliaram-se a produção de AIA in vitro e a promoção de crescimento vegetal pelos isolados em Adesmia latifolia, A. psoraleoides, A. riograndensis e A. tristis. Os isolados bacterianos utilizados são específicos para nodulação em A. latifolia. Os resultados obtidos demonstraram uma produção variável de AIA pelos diferentes isolados. O número de folhas bifoliadas e o comprimento dos brotos não são afetados pelos isolados utilizados neste trabalho. Os efeitos dos isolados de bactérias de nódulos na promoção do crescimento variaram em função da interação com as diferentes espécies de adésmia. O isolado EEL0710 promove maior crescimento em Adesmia latifolia, A. psoraleoides e A. tristis. O isolado EEL1710A promove maior crescimento em A. riograndensis. O nível endógeno de ácido indolacético não apresenta uma relação direta na promoção do crescimento das espécies de Adesmia

Rhizobia are able to increase yield of non-leguminous species through production of phyto-stimulating substances. This study aimed to evaluate the inoculation effect of rhizobia UFRGS Lc348 and VP16 on millet and Sudan grass yield and germination, and verify the enrichment effect of culture medium with tryptophan, which leads on the rhizobium/plant interaction. Experiments in vitro and greenhouse conditions were conducted. In millet, the inoculation with VP16 grown in culture medium with or without tryptophan induces greater length of hypocotyl and epicotyl under in vitro conditions. UFRGS Lc348 treatment induces longer hypocotyls of millet under in vitro conditions. No effects were observed with the millet inoculation in greenhouse. In Sudan grass, inoculation with VP16 enriched with tryptophan increased dry matter in shoots of adult plants. In millet seedlings had achieved an increasing in elongation in vitro conditions, which could represent an adaptive advantage in the search for water and nutrients in the rhizospheric environment during the initial growth of millet. Similarly, if verified in field conditions, Sudan grass had achieved an increasing in greenhouse conditions with the inoculation of tryptophan-enriched VP16, which could be correlated with a significant gain in crop yield. Therefore, these relationships between tryptophan-enriched VP16 and Sudan grass should be verified in subsequent studies under field conditions.

ABSTRACT There is a complex interaction between various components of the soil ecosystem, including microbial biomass and soil chemical contaminants such as heavy metals and radionuclides, which may greatly affect the efficiency of bioremediation techniques. The aim of this study was to investigate microbial capacity to change pH, changes in the metal soluble-exchangeable fraction, and effects of initial heavy metal contents on soil samples in microbial solubilization/immobilization capacity. The soil samples used in this study were collected at a known metal-contaminated site. Three highly metal-resistant bacteria were isolated from rhizosphere soil samples collected on weed species identified as Senecio brasiliensis, Senecio leptolobus, and Baccharis trimera. A completely randomized experimental design in a factorial arrangement was used, with three replicates. In general, with an acid pH, the isolates neutralized the contaminated growth media. In a neutral or basic initial pH, increases in pH were observed in the media, so these bacteria have an alkalizing effect on the growth media. Soluble metal contents were quite different and depend on the microbial species and heavy metal contents in the soil samples. The soluble-exchangeable fraction of metal such as Cu, Zn, Ni, Cr, Cd, Pb, and Ba may be unavailable after inoculation with heavy metalresistant rhizobacteria. A promising approach seems to be the application of inoculants with metal-resistant bacteria in bioremediation of multi-metal-polluted environments to improve the efficiency of this environmentally friendly technology.

This work aimed to evaluate the symbiotic compatibility and nodulation efficiency of rhizobia isolated from Desmodium incanum, Lotus corniculatus, L. subbiflorus, L. uliginosus and L. glaber plants by cross-inoculation. Twelve reference strains and 21 native isolates of rhizobia were genetically analyzed by the BOX-PCR technique, which showed a high genetic diversity among the rhizobia studied. The isolates were also characterized based on their production of indolic compounds and siderophores, as well as on their tolerance to salinity. Fifteen of the 33 rhizobia analyzed were able to produce indolic compounds, whereas 13 produced siderophores. All the tested rhizobia were sensitive to high salinity, although some were able to grow in solutions of up to 2% NaCl. Most of the native rhizobia isolated from L. uliginosus were able to induce nodulation in all plant species studied. In a greenhouse experiment using both D. incanum and L. corniculatus plants, the rhizobia isolate UFRGS Lu2 promoted the greatest plant growth. The results demonstrate that there are native rhizobia in the soils of southern Brazil that have low host specificity and are able to induce nodulation and form active nodules in several plant species.

Seed inoculation with plant growth promoting rhizobacteria (PGPR) is an ideal tool to supply the soil with a high density of beneficial microorganisms. However, maintaining viable microorganisms is a major problem during seed treatment and storage. In this work, an evaluation was made of the effect of bacterial immobilization in nanofibers on the stability (viability and maintenance of beneficial properties) of two potential PGPR, Pantoea agglomerans ISIB55 and Burkholderia caribensis ISIB40. Moreover, the impact of soybean seed coating with nanofiber-immobilized rhizobacteria on bacterial survival during seed storage and on germination and plant growth parameters was determined. Bacterial nanoimmobilization and subsequent seed coating with nanofiber-immobilized rhizobacteria were carried out by electrospinning. The results demonstrate that this technique successfully immobilized P. agglomerans ISIB55 and B. caribensis ISIB40 because it did not affect the viability or beneficial properties of either rhizobacteria. Seed coating with nanofiber-immobilized rhizobacteria improved P. agglomerans ISIB55 and B. caribensis ISIB40 survival on seeds stored for 30 days and contributed to the successful colonization of both bacteria on the plant root. Moreover, seed coating with P. agglomerans ISIB55 increased germination, length and dry weight of the root. Furthermore, seed coating with B. caribensis ISIB40 increased leaf number and dry weight of the shoot. Therefore, the technique applied in the present work to coat seeds with nanofiber-immobilized PGPR could be considered a promising eco-friendly approach to improve soybean production using a microbial inoculant.

Em áreas de várzeas cultivadas, onde o solo é inundado, os rizóbios adaptados ao estresse hídrico podem formar nódulos em leguminosas hibernais, fixar nitrogênio, e até mesmo colonizar plantas de espécies não-legumi- nosas, como gramíneas. Estudos recentes têm mostrado que os rizóbios podem colonizar raízes, caules e folhas de arroz, promovendo o crescimento da planta. A produção de fito-hormônios, principalmente ácido indol acético (AIA), é, possivelmente, o principal mecanismo de promoção de crescimento de arroz por rizóbios. Em várzeas, esses mi- crorganismos podem ser grandes aliados na integração da lavoura de arroz, com o cultivo de leguminosas forrageiras. No cenário orizícola gaúcho, boa parte dos produtores utiliza as áreas de arroz no período de inverno com gado, ou aproveitando a resteva do arroz, ou cultivando azevém, às vezes em consórcio com alguma leguminosa. Neste contexto, durante o inverno, os rizóbios fixariam nitrogênio em simbiose com a leguminosa, promovendo o cresci- mento do pasto, e no verão colonizariam o arroz, estimulando seu crescimento e aumentando o rendimento de grãos. O objetivo desta revisão é relatar estudos que evidenciam a relação dos rizóbios com outras famílias botânicas, como as gramíneas, por diferentes mecanismos de promoção de crescimento, e que em sistemas agrícolas de rotação entre leguminosas e não-leguminosas como o que ocorre em várzeas no Rio Grande do Sul, é possível formar reservatórios de rizóbios no solo, que, por seus diferentes mecanismos de promoção de crescimento de plantas, beneficiem todos os sistemas produtivos desta integração.

The Brazilian state of Rio Grande do Sul has approximately 5.4 million hectares of lowland. The introduction of winter forage legumes, such as white clover, can increase the productivity of these lowland areas through biological nitrogen fixation (BNF). However, this benefit can only occur if the legume is associated with rhizobia that can efficiently fix nitrogen under available soil conditions. The objective of this study was to select rhizobia of Rio Grande do Sul soils, which are efficient in BNF when in symbiosis with white clover, and evaluate the tolerance of this symbiosis under flooded soil conditions. The experiment was conducted in a greenhouse, in soil-filled pots, where 14 isolates were evaluated for nitrogen fixation ability under flooded soil conditions. Each treatment was tested under two soil moisture conditions (flooded and field simulated). Flooding significantly reduced the number and nodule weight as well as the production of dry matter and nitrogen accumulation in the shoots of plants inoculated with rhizobia. The effect of soil flooding on BNF varied according the isolate evaluated. The strains CVII, P3 4, T4 and VP16 exhibited high nitrogen fixation efficiency under flooding conditions, surpassing the nitrogen-added control treatment, on nitrogen accumulation in shoots.

O cornichão é uma leguminosa forrageira perene hiberno-primaveril de grande importância para o Rio Grande do Sul, destacando-se pela capacidade de se manter em solos relativamente ácidos e pouco férteis. Com este trabalho, objetivou-se a seleção de rizóbios para cornichão tolerantes à acidez e ao Al tóxico e eficientes na fixação biológica de N em solos de baixa fertilidade. Foram avaliados 52 isolados de rizóbios de Lotus spp. obtidos de solos de cinco localidades do Rio Grande do Sul. Os rizóbios foram avaliados quanto à diversidade genética, à tolerância a pH 4,2 e ao Al tóxico. Entre os rizóbios tolerantes a fatores de acidez, sete foram avaliados quanto à eficiência simbiótica com plantas, em casa de vegetação, em vasos com solo não estéril. Observou-se alta diversidade genética entre os rizóbios estudados, dos quais 16 foram tolerantes a pH 4,2 e a 50 µM de Al em meio de cultura, produzindo populações da ordem de 10(7) até 10(8) UFC mL-1. Os sete rizóbios testados em casa de vegetação superaram as estirpes atualmente recomendadas para a produção de inoculantes, o que demonstra a existência, em solos do Rio Grande do Sul, de rizóbios tolerantes à acidez do solo e eficientes como fixadores de N em plantas de cornichão.

O cornichão (Lotus corniculatus L.) tem sido apontado como uma das forrageiras mais promissoras para o uso no Rio Grande do Sul. No entanto, pouco se conhece a respeito da interação dessas plantas com os rizóbios nativos em condições de campo. Este estudo visou a avaliar a eficiência das interações entre rizóbios e plantas de Lotus corniculatus cv. 'São Gabriel' em condições de campo. O experimento foi conduzido na Estação Experimental Agronômica da UFRGS com delineamento de blocos ao acaso com quatro repetições. Os tratamentos estudados foram: dois controles sem inoculação (um com a adição de 80kg ha-1 de nitrogênio na forma de uréia e outro sem a adição de nitrogênio); inoculação com rizóbios: estirpes SEMIA 816, recomendada no Brasil, U510, recomendada no Uruguai, U512, em estudo no Uruguai, e quatro isolados de rizóbios nativos (UFRGS Lc322, UFRGS Lc349, UFRGS Lc269 e Iso 7). O isolado UFRGS Lc322 e a estirpe U510 são mais eficientes do que a estirpe SEMIA 816, recomendada para cornichão no país. Além disso, a produção de forragem das plantas inoculadas com o isolado UFRGS Lc322 e a estirpe U510 superou a obtida com a adição de 80kg ha-1 de nitrogênio.The bird's-foot trefoil (Lotus corniculatus L.) has been pointed as one of the most promising forage plants for use in Rio Grande do Sul. However, there is lack of information about the interaction of those plants with the native rhizobia in field conditions. This study aimed to evaluate the efficiency of interactions between rhizobia and plants of Lotus corniculatus cv. 'São Gabriel' in field conditions. The experiment was carried out in the Agronomic Experimental Station (EEA) of the Federal University of Rio Grande do Sul (UFRGS), using random block design with four replications. The treatments were: two controls without inoculation (one with the addition of urea corresponding to 80kg ha-1 of nitrogen and other without nitrogen addition); inoculation with rhizobia: strain SEMIA 816, recommended in Brazil, U150 recommended in Uruguay and U512, being studied in Uruguay, and four rhizobia isolates (UFRGS Lc322, UFRGS Lc349, UFRGS Lc269 e Iso 7). The rhizobia isolate Lc322 and the strain U510 are more efficient than the strain SEMIA 816, which is recommended for bird's-foot trefoil in the country. Furthermore, the forage production of plants inoculated with the isolate Lc322 and the strain U510 surpassed that, with the addition of 80kg ha-1 of nitrogen.

A inoculação de plantas leguminosas com rizóbios é um dos principais métodos biotecnológicos de utilização de micro-organismos em plantas visando à fixação biológica de nitrogênio na agricultura. No entanto, nos últimos anos, vêm sendo observada nesses micro-organismos a capacidade de produção de fitohormônios, principalmente o ácido indol-acético (AIA) e a promoção de crescimento em gramíneas. Dessa forma, os objetivos deste trabalho foram quantificar o ácido indol-acético produzido por rizóbios isolados de alfafa, avaliar o efeito da inoculação desses micro-organismos na germinação de sementes de arroz e realizar a caracterização genética desses isolados. Nove rizóbios isolados de nódulos de alfafa foram avaliados quanto a sua capacidade de produção de equivalentes de AIA e a influência da inoculação desses micro-organismos na germinação e desenvolvimento de plântulas de arroz. Os rizóbios produtores de AIA foram identificados pelo sequenciamento da região do gene 16S do DNAr. A produção de equivalentes ao ácido indol-acético foi observada em todos rizóbios, com valores que variaram de 43,04 a 101,26µg mL-1 em meio de cultura. Com relação à germinação das sementes de arroz, a inoculação com rizóbios acelerou o processo e o crescimento de suas plântulas. Os rizóbios UFRGS Ms58, Ms515, Ms195, Ms205, Ms2010 e 2012 foram identificados como pertencentes à espécie Sinorhizobium meliloti e UFRGS Ms55, Ms72 e Ms75 à espécie Rhizobium sp.The inoculation of leguminous plants with rhizobia is one of the main methods of biotechnological use of microorganisms in order to obtain biological nitrogen fixation in agriculture. However, in recent years it has been attributed to these microorganisms the ability to produce phytohormones, mainly indole acetic acid (IAA), and to promote the growth in grasses. Thus, the objectives of this study were to quantify the indole acetic acid produced by rhizobia from alfalfa and to evaluate the effect of inoculation of these microorganisms on the germination of rice seed and to perform the genetic characterization of these isolates. Nine rhizobia, from nodules of alfalfa, were evaluated for their ability to produce IAA equivalents and for their influence in inoculating these microorganisms on germination and seedling development of rice. Moreover, these rhizobia producers of IAA were identified by the 16S region of DNAr. The equivalent production of indole acetic acid was observed in all tested isolates, with values ranging from 43.04 to 101.26µg mL-1 in culture medium. Regarding the germination of rice seeds, the inoculation with rhizobia accelerated this germination and its growth. Microorganisms UFRGS Ms58, UFRGS Ms515, UFRGS Ms195, UFRGS Ms205, UFRGS Ms2010 and UFRGS 2012 were identified as belonging to the species of Sinorhizobium meliloti. Microorganisms Ms55 UFRGS, UFRGS Ms75 and UFRG Ms72 were identified as belonging to the species of Rhizobium sp.

As leguminosas forrageiras, além de contribuírem para o aumento da oferta de forragem com alto teor de proteína, também são importantes como cobertura vegetal de solos. Entre as leguminosas com grande potencial forrageiro, espécies do gênero Lotus têm se destacado. Este trabalho visou à seleção de rizóbios nativos eficientes em Lotus glaber a partir de amostras de solo de cinco localidades do Rio Grande do Sul. Obtiveram-se 259 isolados de rizóbios, que foram avaliados quanto à morfologia colonial e produção de melanina. Destes, 15 isolados foram selecionados para avaliação da eficiência na fixação simbiótica de nitrogênio em experimento em casa de vegetação e caracterizados geneticamente por comparação do perfil eletroforético dos produtos de amplificação do DNA genômico, por PCR com os oligonucleotídeos iniciadores BOX e ERIC. Apenas cinco isolados produziram melanina. Nove isolados foram mais eficientes do que a estirpe SEMIA 830, que é autorizada para a produção de inoculante para L. glaber no país. Na caracterização genética, observou-se que nenhum isolado apresentou identidade com as estirpes recomendadas, o que demonstra que, nos solos do Rio Grande do Sul, existem rizóbios autóctones eficientes na fixação simbiótica de nitrogênio com L. glaber, podendo ser recomendados para estudos a campo, visando a uma futura produção de inoculantes para estas leguminosas no Brasil.Forage legumes besides contributing to increase the supply of high protein content forage are also good cover for the soil surface. Among the legumes with high potential forage, the genus Lotus has been outstanding. This research aimed to selectnative rhizobia efficient in fixing nitrogen with Lotus glaber, from soil samples of five localities of Rio Grande do Sul. A total of 259 rhizobia isolates were obtained, which were evaluated based on colony morphology and in vitro melanin production. Among them, 15 isolates were selected for the evaluation of the symbiotic nitrogen fixation efficiency in greenhouse experiments and genetically characterized by genomic DNA fingerprinting, PCR amplification with BOX and ERIC primers. Only five isolates produced melanin. Nine isolates were more efficient than strain SEMIA 830, which is authorized for the production of commercial inoculants of L. glaber in Brazil. In relation to the genetic characterization, the isolates have shown no similarity with the commercial strains, indicating that in the soils of Rio Grande do Sul there are autochthonous rhizobia capable of efficient symbiotic nitrogen fixation with L. glaber, which might be recommended for field evaluations, aiming a future production of inoculants for this legume in Brazil.

Variation in rhizobia strains isn’t a desirable fact based mainly on the possibility of unexpected results on legume inoculation. In this work, we studied the variability on phenotypic characteristics and genetic stability of rhizobia strains recommended for soybean inoculation. Variants with stable colony morphology were obtained from Bradyrhizobium japonicum strain SEMIA 5080 and from B. elkanii SEMIA 5019. Variants from SEMIA 587 obtained by another author were also used. The variants differed on colony characteristics, nodulation capacity, nitrogen fixation efficiency and competitive ability for nodule formation in two soybean varieties (Jacui 7 and IAS 5). Symbiotic behavior varied according to plant variety. Only the variants 5019 G and 5019 P differed on the isoenzymatic profile. There were differences in antibiotic resistance between variants from two strains. Correlation between symbiotic characteristics and colony morphology or antibiotic resistance wasn’t conclusive. The results indicate that the variability in rhizobia strains might be an important factor to be considered in strain selection and preservation of cultures for inoculant production.

RESUMO: Embora os rizóbios não apresentem a capacidade de fixar nitrogênio em plantas de arroz, estes podem estimular o crescimento da parte aérea e da raiz, aumentando a absorção de nutrientes, como o nitrogênio, e a produtividade. Com o trabalho, avaliou-se o efeito de rizóbios em promover o crescimento de plantas de arroz em função de doses de nitrogênio (N). Efetuou-se um experimento com vasos contendo solo e plantas da cultivar IRGA 424. As plantas foram inoculadas com oito isolados de rizóbios e adubadas com doses equivalentes a 0, 40, 80 e 160kg N ha-1. Avaliou-se a matéria seca e a quantidade de N acumulada na parte aérea e o perfilhamento das plantas. O efeito do N no crescimento de arroz aumentou com a inoculação de rizóbios. A matéria seca da parte aérea das plantas inoculadas e que receberam, aproximadamente, metade da maior dose de N foi equivalente às que receberam a maior dose desse nutriente e sem inoculação. Além disso, a inoculação com rizóbios aumentou o perfilhamento e a absorção de N. A inoculação de rizóbios em arroz, embora não dispense a adubação nitrogenada, tem potencial para aumentar a produção e a eficiência do uso do N.

ABSTRACT The two main bottlenecks for a successful phytoremediation program are the metal availability in soil and the metal uptake and transfer to shoots of high biomass plants. Several agronomical practices have been tested to boost the bioavailability of metals in soils and accumulation in plants. Here we assessed the feasibility of plant-growth-promoting bacteria (PGPB) isolated from a site contaminated by gold ore processing activities to assist the phytoremediation of As, Cd, and Pb by Sorghum bicolor and mitigate the metal toxicity in plants. The bacteria Kluyvera intermedia, Klebsiella oxytoca, and Citrobacter murliniae were evaluated in single, double, and triple inoculations. They are regarded as metal resistant and were isolated from the rhizosphere of species naturally growing on the metal contaminated site. The treatments comprised two soils (contaminated and non-contaminated) and single (K. intermedia, K. oxytoca, or C. murliniae) or multiple inoculations (K. intermedia + K. oxytoca; K. intermedia + C. murliniae; K. oxytoca + C. murliniae; K. intermedia + K. oxytoca + C. murliniae). Plants were grown for 42 days after inoculation. The results showed that the PGPB K. oxytoca and the combination of K. intermedia + K. oxytoca and K. intermedia + C. murliniae were able to mitigate the metal toxicity in the contaminated soil and hence increase the shoot biomass, with implications to the effectiveness of phytoextraction. The sorghum ability to translocate Cd to shoots in the contaminated soil was enhanced through the single inoculation with K. oxytoca, C. murliniae, and K. oxytoca, as well as by the joint-inoculation with K. oxytoca + C. murliniae, and K. intermedia + K. oxytoca + C. murliniae. Higher accumulation of metals in shoots is a crucial factor in successful phytoextraction. Arsenic and Pb, on the other hand, had their uptake and concentration in roots stimulated by the inoculation. Therefore, regarding these two metals, phytostabilization programs could benefit from the use of the bacteria studied here.

ABSTRACT Rhizobia and associative bacteria promote growth in rice plants (Oryza sativa L.) through a series of mechanisms, but most studies on inoculation have been performed based on inoculation with these bacteria in a separate or singular manner. The objective of this study was to assess the efficiency of single/isolated inoculation and inoculation combined with symbiotic rhizobia from forage legume and with Azospirillum brasilense on promoting growth and the root colonization process in wetland rice. Two rhizobia among four isolates from a greenhouse and a laboratory experiment were selected that efficiently promoted seed germination and rice plant growth in a sterilized substrate and in soil. The two most efficient isolates (UFRGS Vp16 and UFRGS Lc348) were inoculated alone or in combination with a commercial product containing A. brasilense in two field experiments using two wetland rice cultivars over two growing seasons. In the field experiments, these isolates coinoculated with A. brasilense promoted larger increases in the agronomic variables of wetland rice compared to the control without inoculation. Confocal laser microscopy confirmed the presence of inoculated bacteria tagged with gfp (UFRGS Vp16, UFRGS Lc348, and A. brasilense) colonizing the root surface of the rice seedlings, mainly in the root hairs and lateral roots.

A disponibilidade de resíduos de aveia-preta, com relação C:N elevada, resulta em imobilização microbiana de nitrogênio no solo, exigindo cuidados no manejo da adubação nitrogenada da cultura subseqüente. O objetivo deste trabalho foi avaliar as alterações na estrutura da comunidade microbiana ao longo do ciclo do milho, na presença de resíduos de aveia-preta e da aplicação de nitrogênio. Foram coletadas amostras de um Argissolo Vermelho distrófico no dia da semeadura do milho e 46, 62, 88 e 112 dias após a semeadura. O nitrogênio foi aplicado 25 dias e 49 dias após a semeadura. As alterações na comunidade microbiana foram avaliadas mediante relações entre carbono (C) e nitrogênio (N), nitrogênio reativo com ninidrina (N-Nin) e carboidratos (CHO) da biomassa microbiana, além da análise do rDNA fúngico e bacteriano. As diferenças na composição da comunidade microbiana, reveladas pela análise do rDNA, relacionaram-se mais com as relações C:N e C:N-Nin do que com a relação C:CHO. As relações C:N-Nin e C:N e as avaliações do rDNA mostraram um predomínio inicial de população fúngica. Com a aplicação de N, a população bacteriana tornou-se preponderante e, ao final do ciclo do milho, retornou para uma condição semelhante à inicial.The availability of black oat residues, with high C:N ratio, leads to microbial immobilization of soil nitrogen, demanding special strategies to supply nitrogen to subsequent crops. The objective of this work was to evaluate shifts in microbial community structure due to the availability of black oat residues and nitrogen applications during the corn growing season. Soil (Paleudult) samples were collected on the day of the corn seeding and after 46, 62, 88 and 112 days. Nitrogen fertilizer was applied 25 and 49 days after corn seeding. Changes in microbial community were assessed by microbial biomass carbon (C) and nitrogen (N), ninhydrin-reactive N (N-Nin) and carbohydrates (CHO) ratios, besides the analysis of the rDNA of bacteria and fungi. Changes in microbial community shown by rDNA analysis were more related to C:N and C:N-Nin ratios than to C:CHO ratio. The C:N and C:N-Nin ratios and the analysis of the rDNA showed that microbial community was predominantly fungal at the beginning of the evaluation period. After nitrogen application, the bacterial population became preponderant and, at the end of the evaluation period, microbial community turned back to a composition similar to the initial.