Effects of time of nitrate application on nitrate reductase activity, nitrate uptake, and symbiotic dinitrogen fixation in faba bean and pea

Abstract

The effects of increasing concentrations of [Formula: see text] (0, 5, 10, or 15 mol∙m−3) supplied at planting or 7 or 14 days after planting were studied in faba bean (Vicia faba L.) and pea (Pisum sativum L.) inoculated with Rhizobium leguminosarum biovar viceae isolate 175F19. Averaged over all times of [Formula: see text] application, N2 fixation (acetylene reduction) was inhibited significantly more in pea than in faba bean. Times of [Formula: see text] application had little effect on N2 fixation for faba bean. In contrast, N2 fixation in pea was most strongly inhibited when [Formula: see text] was applied at planting and showed a decreasing sensitivity as [Formula: see text] applications were delayed to 7 and 14 days after planting. At all times of [Formula: see text] application, as the levels of [Formula: see text] increased, the proportion of total plant nitrate reductase activity contributed by leaves and roots remained relatively constant in faba bean, but these proportions increased and decreased, respectively, in pea. Nitrate was taken up at higher levels and at a greater rate in pea than in faba bean. The lower capacity for [Formula: see text] uptake in faba bean could contribute to the greater tolerance of the symbiosis to [Formula: see text] compared with that in pea.