Diversidade de rizóbios em Florestas de Araucária no Estado de São Paulo / Rhizobia diversity in Araucaria Forests in São Paulo State, Brazil




Araucaria angustifolia (B.) Ktz has a great social, environmental and economic importance to south and southeastern Brazil, although ecosystems supporting this species have been degraded by human activity, making it an endangered species. The nitrogen cycle has vital importance for life and has a special role in the development and upkeep of forests. The nitrogen input in these systems is dependent on diazotrophic organisms, especially rhizobia, soil bacteria that may nodulate legumes and fix nitrogen in symbiosis with them. The study of rhizobia diversity may support better forest management practices and many techniques are used in these studies, especially the use of trap-plants, field legume nodule collection, bacteria isolation in culture media, phenotypic analysis of the strains and 16S rRNA gene sequencing, all of which were used in this work. From a survey in Campos do Jordão State Park, nine of eleven legume species collected presented nodules, of which five were reported as nodulating for the first time. A total of 212 bacterial strains were isolated from the nodules. There was great variation of nodule shape and great phenotypic richness among isolates. There was variability in the phenotypical diversity of bacteria in each plant, where Galactia crassifolia showed the highest value, while Mimosa dolens showed the lowest one. Of the 212 strains, 55 were able to nodulate common bean and 56 nodulated bracatinga (M. scabrella). The 16S rRNA gene of 196 strains were partially sequenced and classified into eight genotypic groups: Pantoea sp. (2%), Pseudomonas sp. (2%), Bradyrhizobium sp1 (10%), Bradyrhizobium sp2 (7%), Rhizobium sp. (1%), Burkholderia sp1 (14%), Burkholderia sp2 (26%) and Burkholderia sp3 (38%). Phylogenetic analysis showed that most of the groups belong to bacteria genera related to rhizobia. There was variability in the bacterial diversity related to the isolated plants, where G. crassifolia showed the highest value, being considered the most promiscuous, while Acacia dealbata and M. dolens presented the lowest values, and were considered the most specific ones. The phenotypic analysis of rhizobia was shown to be inappropriate for taxonomy, since the phenotypic results were different from the genotypic ones. Araucaria Forests with different levels of human interference (Preserved Forest, Planted Forest and Recovering Forest) were compared using cowpea, peanut, soybean, bracatinga, maricá (M. bimucronata) and angico (Parapiptadenia rigida) as trap-plants. Maricá was the most efficient in rhizobia capture, while bracatinga and cowpea showed less efficiency and the others failed. A total of 78 strains were isolated and classified into six genotypic groups: Pseudomonas sp. (3%), Xanthomonas sp. (1%), Ralstonia sp. (6%), Herbaspirillum sp. (4%), Burkholderia sp1 (29%) and Burkholderia sp3 (57%), of which three are the same as previously classified. Most of these groups are related to known rhizobia or other endophytic bacteria. The Recovering Forest showed the highest diversity of isolated bacteria, while Planted Forests and Preserved Forest showed similar indeces. β-rhizobia were predominant in the studied areas.


Árvores florestais pinheiros reflorestamento Áreas de conservação forest trees biodiversidade pines nitrogen-fixing bacteria planted forests bactérias fixadoras de nitrogênio forests – "mata altântica" (atlantic forest) biodiversity conservation areas florestas – mata atlântica

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