02245naa a2200301 a 450000100080000000500110000800800410001910000160006024500900007626000090016652014510017565000140162665000080164065000100164865000150165865000120167365000290168565000160171465000160173065000160174665000230176265000140178565300290179965300140182865300160184270000190185877300660187714577602024-04-17       1989    bl uuuu     u00u1 u    #d1 aHUNGRIA, M.  aAcetylene reduction, hydrogen evolution and nodule respiration in Phaseolus vulgaris.  c1989  aIn an experiment performed under greenhouse conditions, four cultivars of Phaseolus vulgaris L. (Venezuela-350; Aroana; Moruna; Carioca) were inoculated with three Rhizobium leguminosarum biovar phaseoli strains (C-05; C-40 = CIAT 255; C-89 = CIAT 55) and were fertilized with an N-free mineral nutrient solution. The plants were harvested 25, 40, and 55 days after emergence and the following paramenters were evaluated: Nitrogenase activity of nodulated roots, H2 evolution by the nodules; relative efficiency of nitrogenase; respiration rates of nodulated roots and detached nodules; dry weight and total N of stems, leaves, pods, roots, and nodules. Generally the bean cultivar, Rhizobium strain, had an effect and there was an interaction effect with both symbiotic partners, on all parameters. On average, nodules represented 23% of total root respiration but the best symbiotic combinations showed lower ratios of C respired to N fixed. The maximum N-assimilation rate (between 40 and 55 days after emergence) of 11.93 mg N plant-1 day-1 occurred with the symbiotic combination of Carioca × C-05, while the poorest rate of 0.55 mg N plant-1 day-1 was recorded with Venezuela-350 × C-89. The best symbiotic combinations always showed the highest relative nitrogenase efficiency, but the differences in N2-fixation rates cannot be explained solely in terms of conservation of energy by recycling of H2. This requires further investigation.  aacetylene  aAra  abeans  anodulation  aFeijão  aFixação de Nitrogênio  aNitrogenase  aNitrogênio  aNodulação  aPhaseolus Vulgaris  aRhizobium  aAcetylene reducion assay  aFeijoeiro  aHydrogenase1 aRUSCHEL, A. P.  tBiology and Fertility of Soilsgv. 7, n. 4, p. 351-358, 1989.