FIG. 4.

N₂O uptake from root systems of intact plants (A and B) and decapitated root systems (C) inoculated with the wild-type strain or the nosZ mutant of Bradyrhizobium japonicum USDA110. Initial gas phases were adjusted to approximately 800 ppm (A) (intact plant) and 0.34 ppm (B [intact plant] and C [decapitated root system]) of N₂O in air. Soybean plants that harbored 0.26 to 0.30 g (A), 0.15 to 0.22 g (B), or 0.18 to 0.36 g (C) of nodules (fresh weight per plant) were examined by a test tube system (see the text). Triplicate determinations were carried out, except that data for USDA110ΔnosZ inoculation in panel A show means of duplicate determinations. Error bars, SDs.