Microbial quality of soil from the Pampa biome in response to different grazing pressures

The aim of this study was to evaluate the impact of different grazing pressures on the activity and diversity of soil bacteria. We performed a long-term experiment in Eldorado do Sul, southern Brazil, that assessed three levels of grazing pressure: high pressure (HP), with 4% herbage allowance (HA), moderate pressure (MP), with 12% HA, and low pressure (LP), with 16% HA. Two reference areas were also assessed, one of never-grazed native vegetation (NG) and another of regenerated vegetation after two years of grazing (RG). Soil samples were evaluated for microbial biomass and enzymatic ( -glucosidase, arylsulfatase and urease) activities. The structure of the bacterial community and the population of diazotrophic bacteria were evaluated by RFLP of the 16S rRNA and nifH genes, respectively. The diversity of diazotrophic bacteria was assessed by partial sequencing of the 16S rDNA gene. The presence of grazing animals increased soil microbial biomass in MP and HP. The structures of the bacterial community and the populations of diazotrophic bacteria were altered by the different grazing managements, with a greater diversity of diazotrophic bacteria in the LP treatment. Based on the characteristics evaluated, the MP treatment was the most appropriate for animal production and conservation of the Pampa biome

Isolation and selection of rhizobia effective for symbiotic fixation of nitrogen in vetch (Vicia sativa) and growth promotion in rice cultivars and white oat

Os rizóbios são bactérias do solo que realizam simbiose com plantas leguminosas e fixam nitrogênio atmosférico. Estas bactérias também são conhecidas por colonizar endofiticamente e produzir substâncias estimuladoras que influenciam no crescimento e no desenvolvimento de plantas não leguminosas. Para aumentar a eficiência na promoção de crescimento vegetal, estuda-se a utilização de plantas leguminosas e não leguminosas em consórcio ou em sucessão, bem como a inoculação conjunta de rizóbios. O presente estudo tem como objetivo isolar e selecionar rizóbios simbiontes eficientes na fixação de nitrogênio em ervilhaca (Vicia sativa) e avaliar o potencial destas bactérias na promoção de crescimento em cultivares de arroz (Oryza sativa) e em aveia branca (Avena sativa). Sendo assim, os rizóbios foram caracterizados quanto à morfologia colonial, capacidade de solubilizar fosfato tricálcico (Ca3(PO4)2), e de produzir ácido indol-acético (AIA) com e sem adição de triptofano no meio de cultura. Em casa de vegetação, os rizóbios foram autenticados e avaliados quanto à eficiência na fixação simbiótica de nitrogênio em ervilhaca. De acordo, com a capacidade de solubilizar fosfato tricálcico, produção de AIA com e sem adição de triptofano e a eficiência simbiótica, foram selecionados cinco rizóbios (UFRGS Vs6, UFRGS Vs12, UFRGS Vs16, UFRGS Vs26 e UFRGS Vs30) e avaliou-se o efeito destas bactérias sobre a germinação e a capacidade das mesmas em promover o crescimento vegetal em cultivares de arroz e de aveia, em casa de vegetação e posterior caracterização genética. Todos rizóbios isolados produziram ácido indol-acético em meio de cultura sem e com adição de triptofano, 19 solubilizaram fosfato tricálcico em meio de cultura. Em relação à eficiência dos rizóbios na fixação simbiótica de nitrogênio destacou- se o isolado UFRGS Vs30 com índice de eficiência relativa de 50%. Os rizóbios UFRGS Vs26 e UFRGS Vs30 estimularam a germinação das sementes de arroz IRGA 424RI e os rizóbios UFRGS Vs6 e UFRGS Vs16 de aveia. Em plantas de aveia, os rizóbios UFRGS Vs6, UFRGS Vs16, UFRGS Vs26 e UFRGS Vs30 aumentaram a massa da raiz. Em plantas de arroz os rizóbios UFRGS Vs12, UFRGS Vs16 e UFRGS Vs30 promoveram incremento na massa seca da parte aérea das três cultivares estudadas e da massa seca de raiz das cultivares IRGA 430 e IRGA 424. Anteriormente não haviam sido descritas espécies de Rhizobium phaseoli e Rhizobium vallis capazes de nodular e/ou fixar nitrogênio em ervilhaca.Rhizobia are soil bacteria that perform symbiosis with leguminous plants and fix atmospheric nitrogen. Those bacteria are also known for colonizing - by endophytic form – and produce substances that promote growing and development of non-leguminous plants. To increase production efficiency in vegetable growing, we have been studying utilization of leguminous plants and non-leguminous plants in consortium or succession as well as inoculation of rhizobia alongside. This research have the objective of isolate and select rhizobia efficient to fix nitrogen in vetch (Vicia sativa) – by symbiosis - and evaluate potential of those bacteria increase growing of rice cultivars (Oryza sativa) and white oat (Avena sativa). Therefore, rhizobia were characterized about colony morphology, their ability to solubilize tricalcium phosphate (Ca3(PO4)2) and produce indole acetic acid (AIA), with or without addition of tryptophan in growing medium. In the greenhouse, rhizobia were authenticated and evaluated about of their efficiency in fixing nitrogen in vetch through symbiosis. It was selected five potential rhizobia (UFRGS Vs6, UFRGS Vs12, URFGS Vs16, UFRGS Vs26 and UFRGS Vs30). We evaluated the effect of selected rhizobia on seed germination, ability of producing vegetable growing in cultivars of rice and oat in the greenhouse, and further genetic description. All isolated rhizobia produced indole acetic acid in the growing medium without and with addiction of tryptophan, 19 solubilized tricalcium phosphate in growing medium. Related of rhizobia efficiency in fixing by symbiosis, the isolated UFGRS Vs30 stood out with efficiency level of 50%. Rhizobia UFRGS Vs26 and UFRGS Vs30 increased seeds germination of rice IRGA 424RI and rhizobia UFRGS Vs6 and UFRGS Vs16 increased it in oat. Rhizobia UFRGS Vs6, UFRGS Vs16, UFRGS Vs26 and UFRGS Vs30 increased dry mass of root of oat plants. Concerning rice plants, rhizobia UFRGS Vs12, UFRGS Vs16 and UFRGS Vs30 increase dry aerial mass in three cultivars of rice and the dry mass root of cultivars IRGA 430 and IRGA 424. There were not species of Rhizobium phaseoli and Rhizobium vallis able to nodulate or fix nitrogen in vetch