Diversidade de rizóbios na estruturação de comunidade de plantas nativas da Floresta Atlântica

Abstract

This study aimed to evaluate the influence of the diversity of nitrogen-fixing bacteria on the productivity of 6 tree species native to the Atlantic Forest in microcosm conditions. Two experiments were conducted in a glasshouse at Embrapa Agrobiologia. The first experiment simulated a community with 3 legume and 3 non-legume species and it was carried out in trays containing 45 kg of substrate (soil:sand:vermiculite v:v:v). These species were tested individually in 1.5 kg pots in the second experiment. Both experiments followed a randomized block design, with 6 replicates. The following treatments were tested: inoculation of plants with two levels of rhizobial richness (3 and 9 strains), and two controls, one receiving mineral fertilization and another that received neither inoculation or fertilization. The rhizobia inoculated are recommended for the legume species used in the experiments, that is, Albizia pedicellaris, Piptadenia gonoacantha, and Pseudopiptadenia contorta. Plant height was measured at 30, 60, 90, 120, 150 and 180 days after transplanting. Plants were collected after 180 days and dried at 65 ° C until constant weight and the masses of dry shoot and root, as well as shoot total N, were measured. Further, nodule occupancy was evaluated. The levels of diversity of nitrogen fixing bacteria for some species of legumes had a positive effect on average height , accumulation of root mass and leaf N content . This effect was not observed for the variable dry matter of shoots. Additionally, we isolated and characterized, phenotypic and genotypically, bacteria isolated from nodules Pseudopiptadenia contorta , Albizia pedicellaris and Piptadenia gonoacantha. The Morphophysiological characterization demonstrated considerable diversity among the isolates. PCR amplification using the primer BOX- A1R revealed a high genotypic diversity among isolates. Seven major groups were formed. The molecular analysis of 16S rRNA gene sequences revealed that these bacteria belong to the genera Burkholderia, Bradyhrhizobium, Rhizobium and Mesorhizobium. A group of isolates did not cluster closely to species already described, thus presenting a potential for the description of new species. Nodule occupancy by the inoculated bacteria in forest legume Albizia pedicellaris and Piptadenia gonoacantha in the microcosm differed from that in individual pots.