Aims: The objective of this work was to isolate and characterize indigenous rhizobia from coal-mining areas able to efficiently nodulate and fix nitrogen in association with Calopogonium mucunoides (calopo). Methods and Results: Isolation, authentication and morphological, biochemical and molecular characterization of the autochthonous rhizobia were performed and their symbiotic efficiency (SE) evaluated. Efficient rhizobial isolates suitable for the inoculation of calopo in coal-mining regions were obtained. A total of 30 isolates were obtained after nodulation authentication, of which five presented high SE with plant-growth promoting traits such as indole-3-acetic acid production, phosphate solubilization and biofilm formation. These isolates were identified as belonging to Bradyrhizobium, Pseudomonas and Rhizobium. Conclusions: Bradyrhizobium sp. A2-10 and Pseudomonas sp. A6-05 were able to promote calopo plant growth using soil obtained from coal-mining degraded areas, thus indicating their potential as inoculants aiming at land reclamation. Significance and Impact of the Study: To our knowledge, this is the first report of Pseudomonas nodule formation in calopo. Furthermore, the results demonstrated that autochthonous rhizobia obtained from degraded soils presented high SE in calopo and possess a wide range of plant-growth promoting traits. Ultimately, they may all contribute to an increased leguminous plant growth under stress conditions. The selected rhizobia strains may be used as inoculants and present a valuable role in the development of strategies aiming to recover coal-mining degraded areas. Bacterial inoculants would greatly reduce the use of often harmful nitrogen fertilizers vastly employed in revegetation programmes of degraded areas.the removal and deposition of soil, the mixing of other materials, and the removal of native vegetation from the impacted sites. An example of coal-mining pollution is seen in the Santa Catarina coal basin, located in southern Brazil, which has been classified as critical (Stahl et al. 2002). Soils from these areas are highly degraded, with Journal of Applied Microbiology 126, 523--533
No Brasil, a fim de minimizar o impacto da exploração de espécies arbóreas para fins comerciais em florestas nativas, plantios florestais têm sido implantados, majoritariamente, com espécies exóticas. A avaliação de tais cultivos quanto ao impacto proporcionado ao ambiente em atributos que podem garantir sua produtividade tem recebido maior atenção nos últimos anos, enquadrando-se neste contexto, o estudo de atributos microbiológicos. Deste modo, este trabalho teve como objetivo avaliar os impactos de plantios florestais de pinus e araucária sobre os atributos microbiológicos do solo e a estrutura da comunidade bacteriana, que podem funcionar como indicadores da qualidade do solo. Para tanto, foram coletadas amostras de solo em três áreas na Floresta Nacional de Três Barras (FLONA), Santa Catarina (SC): uma área de floresta nativa (F), uma área de reflorestamento com araucária (A) e outra com pinus (P). Posteriormente, foi realizada a caracterização química e física do solo, além das análises microbiológicas: respiração basal, atividade da enzima β-glucosidase e fosfatase ácida, e análise de composição da comunidade bacteriana por PCR-DGGE. Os solos das três áreas de estudo apresentaram baixa fertilidade, destacando a importância dos microrganismos para a manutenção desses ambientes. A atividade da enzima β-glucosidase e da fosfatase ácida foi maior nas áreas F e A, sugerindo maior presença de microrganismos importantes para a ciclagem de nutrientes. A análise da estrutura da comunidade bacteriana demonstrou que há uma baixa divergência entre as áreas de pinus e araucária. Pode-se concluir que, com base nos atributos microbiológicos e na estrutura de comunidades bacterianas do solo, em plantios florestais da Mata Atlântica, a araucária destaca-se como melhor alternativa para reflorestamento, visando à manutenção da qualidade do solo.
The intense exploitation of coal deposits in Southern Brazil has caused severe degradation problems in extensive areas. In order to recover such areas, the use of revegetation with species adapted to disturbed environments and with the capacity to establish mutual relationships with microorganisms have been of great value. The objective of this study is to characterize plant-root symbioses in two grass-legume (Calopogonium mucunoides with Brachiaria decumbens and Vicia sativa with Brachiaria decumbens) consortia inoculated with soil of the Carboniferous Basin in the state of Santa Catarina. Areas evaluated were at different stages of land reclamation and the influence of those consortia on the occurrence of rhizobia, arbuscular mycorrhizal fungi, and in the community of endophytic bacteria were evaluated. The study was done in two independent experiments in a completely randomized design, with five replications; done under greenhouse condition. There were seven treatments-five inoculated (with soil obtained from areas of 2, 4, 6 and 12 years of recovery, and a reference area) and two control treatments without inoculation (with low and high concentrations of mineral nitrogen). After 50 days of implantation, soil and plant material were collected to characterize root symbioses by nodule counting, nitrogen fixing bacteria isolation, mycorrhizal occurrence (%), and characterization of root endophytic bacterial communities. Only the calopogonium-brachiaria consortium was able to nodulate with rhizobia from the recovering coal mining areas. Arbuscular mycorrhizal fungi (AMF) and endophytic bacteria occur in the vetch-brachiaria and calopogonium-brachiaria consortia regardless of the time of recovery. The microbial communities present in soils with different stages of recovery are more efficient in promoting plant growth in the calopogonium-brachiaria consortium and this behavior may be associated with the calopogonium's ability to associate with autochthonous rhizobia.
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