Caracterização e seleção de rizóbios noduladores de leguminosas florestais para recuperação de áreas contaminadas por petróleo

Abstract

Nitrogen-fixing Rhizobium bacteria in nodules on the roots of leguminous forest trees are an important means of maintaining such plants in nutrient-poor tropical soils. These bacteria are used in agroflorestry systems to recover the fertility and sustainability of degraded soils. This study aimed to characterize 28 isolates of rhizobia isolated from petroleum residues contaminated soils according to its phenotipic diversity and nitrogen fixation potential. The isolates were phenotipically characterized in yeast-mannitol minimal medium supplemented with 8 different carbon sources and the data was analysed through numerical cluster analysis, comparing with strains belonging to the bacterial species which nodulate legume trees. At a similarity of 69,5% most isolates formed great groups with Rhizobium, Sinorhizobium and Burkholderia . A second grouping with 4 isolates was formed at a similarity of 70% with the bacteria Cupriavidus taiwanensis and Azorhizobium doebereinerae. The isolate L79 presented similarity of 95% with the bacteria Azorhizobium doebereinerae. The efficiency of selected isolates was tested in experiments arranged in factorial randomized block design with three replicates. Treatments consisted of 13 selected isolates and three control treatments: (1) plants inoculated with the commercial isolates; (2) plants grown without nitrogen and non inoculated and (3) nitrogen supplied plants. Quantitative results were analyzed by statistic software SISVAR. The analyzed variable was shoot dry weight and nodule weight to calculate the efficiency of the isolates. All the three legume tree presented statistical difference about shoot and nodule dry weight. Six isolates showed higher efficiency than commercial recommend strains to be inoculated in two species of legume trees (Mimosa caesalpinaeifolia Benth and Albizia saman (Jacq.) Merr).