Nitrogen fixation and nitrate reduction in the root nodules of legumes

Published data on, and hypotheses regarding the effect of NO−3on functioning of legume root nodules are reviewed. It is concluded that a short‐term reversible effect of NO−3may act via an increased resistance to O2diffusion in nodules; this is coupled to decreased bacteroid respiration. For longer exposures to NO−3nodule activity is irreversibly lost, but how this relates to carbohydrate deprivation or NO‐2accumulation is unclear. Complicating factors include denitrification reactions and the interaction of NO−2with leghaemoglobin.