Diversidade de rizóbios isolados de diferentes sistemas de uso da terra na Amazônia

Abstract

Bèlow ground microbiota is thought to have a close relationship with above ground biodiversity. Besides, lost ofmicrobial diversity can lead to a lost of function reducing ecosystem sustaintability. BNF is among the most important soil functions, especially those performance by rhizobia symbiosis with legumes species. Aiming to evaluate densities as well as phenotypic, genetic and symbiotic diversity ofrhizobia populations at soil samples collected from three sites of each one ofthe following land use systems (LUS) in Amazon region: disturbed forest, fàllow, pasture, crops and agroforestry systems, greenhouse and laboratory assays were carried out. Siratro (Macroptilium atropurpureum Urb.) and cowpea (Vigna unguiculata (L.) Walp) were used as trap hosts for rhizobia strains, being the former also used to determine rhizobia most probable numbers and population efficiencies at the LUS. Rhizobia were also isolated from trap hosts and from non inoculated bean plants and other leguminous species which were found nodulatíng with native populations at some sites. Ali isolates were characterized culturally on YMA médium. Ali bean and cowpea isolates and some siratro isolates were characterized by polyacrilamide gel electrophoresis (SDS-PAGE) oftotal proteins. Genetic analysis ofbean isolates was made by comparison of restriction pattems with diflèrent enzymes to amplifíed 16S rRNA fragments (RFLP). At greenhouse conditions 26 cowpea isolates and 14 bean isolates were evaluated for the biological nitrogen fixation (BNF) efficiency to their homologous hosts. There was effect ofLUS on densities and efficiency ofrhizobia populations trapped by siratro. Bean isolates showed the same cultural characteristics on YMA but were highly mscriminated by SDSPAGE oftotal proteins and RFLP patterns. Most ofthem were highly efficient in BNF and even higher than recommended strain CIAT 899. Great phenotypic and symbiotic diversity was also found among cowpea isolates most of them showing superior efficiency to recommended strain BR 2001. The different LUS presented high diversity ofrhizobia populations. Cultural diversity calculated by Shannon-Weaver index decreased in the order: forest > agroforestry system> pasture> fallow > crops.