Dinitrogen fixation by surface peat and Sphagnum in an ombrotrophic bog

Annual dinitrogen fixation at the surface of ombrotrophic Thoreau's Bog in eastern Massachusetts, U.S.A., is estimated at 1.0 g N∙m 2 . The rates of acetylene reduction are lower but still significant in the dark, suggesting that fixation is carried out both photosynthetically and heterotrophically. The ratio 15 N 2 fixed: C 2 H 2 reduced was 1 mol: 3.5 mol in in vitro calibration experiments. Dinitrogen fixation is ecologically important in this bog as it exceeds the only other known input of nitrogen, namely deposition of NO 3 − and NH 4 + in bulk precipitation.