Tripartite symbiosis of Sophora tomentosa, rhizobia and arbuscular mycorhizal fungi

ABSTRACT Sophora tomentosa is a pantropical legume species with potential for recovery of areas degraded by salinization, and for stabilization of sand dunes. However, few studies on this species have been carried out, and none regarding its symbiotic relationship with beneficial soil microorganisms. Therefore, this study aimed to evaluate the diversity of nitrogen-fixing bacteria isolated from nodules of Sophora tomentosa, and to analyze the occurrence of colonization of arbuscular mycorrhizal fungi on the roots of this legume in seafront soil. Thus, seeds, root nodules, and soil from the rhizosphere of Sophora tomentosa were collected. From the soil samples, trap cultures with this species were established to extract spores and to evaluate arbuscular mycorhizal fungi colonization in legume roots, as well as to capture rhizobia. Rhizobia strains were isolated from nodules collected in the field or from the trap cultures. Representative isolates of the groups obtained in the similarity dendrogram, based on phenotypic characteristics, had their 16S rRNA genes sequenced. The legume species showed nodules with indeterminate growth, and reddish color, distributed throughout the root. Fifty-one strains of these nodules were isolated, of which 21 were classified in the genus Bacillus, Brevibacillus, Paenibacillus, Rhizobium and especially Sinorhizobium. Strains closely related to Sinorhizobium adhaerens were the predominant bacteria in nodules. The other genera found, with the exception of Rhizobium, are probably endophytic bacteria in the nodules. Arbuscular mycorrhizal fungi was observed colonizing the roots, but arbuscular mycorhizal fungi spores were not found in the trap cultures. Therefore Sophora tomentosa is associated with both arbuscular mycorhizal fungi and nodulating nitrogen-fixing bacteria.

Nursery growth and rhizobia symbiosis of scandent Leguminosae species native to the Amazon region / Crescimento e simbiose com rizóbios em casa de vegetação de espécies de Leguminosae escandentes nativas da região Amazônica

A great number of species and individuals of scandent legumes establishing symbiosis with nitrogen fixing bacteria occurs in the Amazon Forest. These symbiosis probably play an important role in contributing to nitrogen incorporation in this ecossystem. The objectives of this study were to evaluate the growth of eight species of scandent legumes in five nursery substrates; to compare nodulation with rhizobia strains introduced or native to these substrates; and to characterize phenotypically and genetically these rhizobia. The experiment was carried out in a completely randomized design with five replications. Five to seven months after seedling emergency, according to the legume species, growth and nodulation parameters were determined. Rhizobia identification of strains was carried out by 16S rRNA gene partial sequencing. The survival of seedlings after the transplanting varied from 93 to 98%, in Ultisol (Argissolo in Brazilian classification), collected in primary forest, and fertilized with all nutrients, except nitrogen (ULTfert); and in a clay and sand mixture, in a ratio 3:2 (CONV), respectively. Species with height superior to 30 cm, in general, grew better in substrates with higher fertility: ULTfert and Humic Gley soil (HG). Seven out of the eight species were able to nodulate. The percentage of nodulation per substrate was: SAND, washed sand with mixed inoculum of 100 rhizobia strains plus fertilization (100), HG (80), CONV (100), ULT, A-horizon of red-yellow Ultisol collected in the Ducke Forest Reserve (Manaus) (44), and ULTfert (55%). Bradyrhizobium spp. were isolated from nodules of all species and substrates. Burkolderia fungorum was isolated from Dalbergia inundata. For Dalbergia riedelli and Dalbergia inundata, this is the first report on the identification of symbiotic strains. Scandent legumes present high survival of seedlings in nursery, and develop better in substrates with higher fertility, and generally present symbiosis with [...].

Um grande número de espécies e indivíduos de leguminosas escandentes estabelecendo simbiose com bactérias fixadoras de nitrogênio ocorrem na floresta Amazônica. Estas simbioses provavelmente desempenham importante papel, contribuindo para incorporação de nitrogênio neste ecossistema. Os objetivos deste trabalho foram avaliar o crescimento de oito espécies de leguminosas escandentes em cinco substratos no viveiro; comparar a nodulação com as estirpes de rizóbio introduzidas ou nativas destes substratos; e caracterizar esses rizóbios fenotípica e geneticamente. O experimento foi conduzido em delineamento inteiramente casualizado com cinco repetições. Cinco a sete meses após a emergência das mudas parâmetros de crescimento e nodulação foram determinados. A identificação das estirpes de rizóbios foi feita pelo sequenciamento parcial do gene 16S rRNA. A sobrevivência das mudas após o transplante variou de 93 a 98%, em um Argissolo (Ultisol de acordo com a classificação da USDA), coletado em floresta primária e adubado com todos os nutrientes, exceto nitrogênio (ULTfert), e na mistura argila e areia, na proporção 3:2 (CONV), respectivamente. Espécies que apresentaram altura superior a 30 cm, no geral, cresceram melhor nos substratos de maior fertilidade: ULTfert e solo Glei Húmico (GH). Das oito espécies estudadas, sete nodularam. A porcentagem de nodulação por substrato foi: AREIA, areia lavada com inóculo misto de 100 estirpes de rizóbio mais adubação (100), GH (80), CONV (100), ULT, horizonte A de Argissolo vermelho-amarelo coletado na Reserva Florestal Ducke (Manaus) (44) e ULTfert (55%). Bradyrhizobium spp. foram isolados de nódulos de todas as espécies e substratos. Burkolderia fungorum foi isolada de Dalbergia inundata. Este é o primeiro relato de identificação de estirpes simbióticas para Dalbergia riedelli e Dalbergia inundata. Leguminosas escandentes apresentaram alta sobrevivência de mudas em casa de vegetação e desenvolveram-se [...]