Oxygen limitation of N2 fixation in various legume symbioses

Two O2 ramping techniques (linear versus exponential) were used to investigate the response of H2 evolution from intact nodules of soybean (Glycine max (L.) Merr. 'Maple Arrow'), stem-girdled soybean, pea (Pisum sativum L. 'Juneau'), and common bean (Phaseolus vulgaris L. 'Ex Rico 23') to increasing O2 concentrations from 20 to 100% over a 30-min period. The data indicate symbiosis-specific responses to the two ramps, and possible implications for determination of O2 limitation of N2 fixation. Key words: Hydrogen evolution, legume, nitrogen fixation