Acetylene reduction,hydrogen evolution and nodule respiration in Phaseolus vulgaris |
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Authors: | M Hungria A P Ruschel |
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Institution: | (1) EMBRAPA-UAPNPBS, Km 47, Antiga Rio-S. Paulo, 23851 Seropédica, Rio de Janeiro, Brazil;(2) EMBRAPA-CNPAF, Cx. Postal 179, 70000 Goiânia, Goiás, Brazil |
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Abstract: | Summary In 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. |
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Keywords: | Phaseolus vulgaris Rhizobium Nitrogenase Hydrogenase Nodulation Acetylene reduction assay (ARA) |
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