| Résumé | Estimated values for the respiration associated with symbiotic nitrogen fixation in Pisum sativum L. were independent of irradiance, temperature, plant age, and CO₂ concentration, despite large variation in the total rates of C₂H₂ reduction and root + nodule respiration. Similar values were also found in Phaseolus vulgaris L., Vicia faba L. and Glycine max (L.) Merr. Among all combinations of four Pisum cultivars with four Rhizobium leguminosarum inoculants only the plant genotype significantly affected the fixation-linked respiration, although both plant and bacterial types significantly influenced the total rate of C₂H₂ reduction. On the basis of measured rates of H₂ evolution and C₂H₂ reduction, or total nitrogen gain in the same system, the least respiration per unit of ammonia produced symbiotically was estimated as 4.8 to 6.9 moles CO₂ (mole NH₃)⁻¹ in Laxton's Progress and the greatest as 9.3 to 13.3 moles CO₂ (mole NH₃)⁻¹ in an Indian cultivar, as compared to a theoretical minimum respiration requirement of 4.7 moles CO2 (mole NH₃)⁻¹ in peas. |
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