Hydrogen production and nitrogen fixation by <i>Oscillatoria thiebautii</i> during in situ incubations1,2

Abstract

We have examined net hydrogen production, acetylene reduction, and 15 N 2 fixation by the marine nitrogen fixer, Oscillatoria thiebautii, using both “standard” conditions and ultraclean and in situ techniques. Rates of hydrogen production and acetylene reduction appeared to be independent of incubation technique. This finding contrasts with previous reports that marine nitrogen fixers might be very sensitive to handling or trace metal contamination. Hydrogen production was highest at the surface and decreased sharply with depth, and no production (or acetylene reduction) was observed during dark incubations. Hydrogen production rates were two to three orders of magnitude lower than nitrogen fixation rates. In addition, the ratio of acetylene reduction to nitrogen fixation determined on one date, 4.1(±1.6): 1, is consistent with the hypothesis that hydrogen is not released from O. thiebautii in significant amounts.