Mining activities promote severe environmental degradation in many parts of the world, and revegetation techniques with diverse plant species have been used for rehabilitation of these areas. Studies on the occurrence, efficiency and diversity of key microbial groups such as leguminosae-nodulating, nitrogen fixing bacteria (LNNFB) are essential because they are involved in nutrient cycling processes and, therefore, to the sustainability of these areas. Aiming to evaluate the efficiency and phenotypic diversity of LNNFB, soil samples were collected from different bauxite mining areas with distinct rehabilitation strategies and chronosequences in the summer of 1999. With these materials we installed experiments using bean and cowpea as trap species under greenhouse conditions. At flowering, the plants were harvested and the shoot dry weight, nodule number, nodule weight, nitrogenase activity, and phenotypic diversity of LNNFB isolates evaluated by culture characterization on 79 medium. There was no influence of the different rehabilitation strategies on the efficiency of LNNFB populations in promoting bean growth. After phenotypic characterization of 328 bean and 420 cowpea LNNFB isolates, it was found that the latter is better suited than bean for studies evaluating LNNFB nodulation, efficiency and diversity in these areas. Mining strongly decreases the LNNFB diversity, while there is little effect on nodulation of trap plants. Rehabilitation strategies contribute to increase LNNFB diversity in bauxite mined soils, mainly when legume species were introduced.
root symbiosis; disturbed soil; trap plants; rhizobia
