Calorimetry of nitrogenase-mediated reductions in detached soybean nodules.

Heat evolved by isolated soybean (Glycine max cv Clark) nodules was measured to estimate more directly the metabolic cost associated with the symbiotic N(2) fixation system. A calorimeter constructed by modifying standard laboratory equipment allowed measurement on 1 gram of detached nodules under a controlled gas stream. Simultaneous gas balance and heat output determinations were made.

N(2) Fixation by Azospirillum brasilense and Its Incorporation into Host Setaria italica.

Growth and nitrogen fixation were followed during the life cycle of Setaria italica (foxtail millet) inoculated with Azospirillum brasilense in controlled-environment growth chambers. The plants were fertilized at seeding with a limiting amount of combined nitrogen and maintained with an N-free mineral solution. During maturation of the plants, substantial nitrogenase activity, measured by acetylene reduction, developed in the rhizosphere, with total fixation estimated to be equivalent to 20% of the N in the inoculated plants.