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Evolution of Earth's Biogeochemical Cycles: O2's Role in Nitrogen Transformation

This study explores the influence of oxygen on Earth's biogeochemical cycles, particularly the nitrogen cycle, through a generalized biosphere model. Oxygen’s emergence enabled the conversion of NH4+ to NO3-, facilitating its reduction to N2. The research examines historical shifts in nitrogen cycling as major barriers to planetary oxidation were overcome, leading to a new ecological equilibrium. It discusses feedback mechanisms during Oceanic Anoxic Events, denitrification processes, and the impact of oxygen on primary production and nitrogen fixation, supported by evidence from paleorecords.

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Evolution of Earth's Biogeochemical Cycles: O2's Role in Nitrogen Transformation

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  1. Fig. 1. A generalized biosphere model showing the basic inputs and outputs of energy and materials P. G. Falkowski et al., Science 320, 1034 -1039 (2008) Published by AAAS

  2. O2-mediated Mn -mediated Fe-mediated S-mediated N-mediated H2 or C-mediated Mn2+ NH4+ Fe2+ HS- CH4 H2 [CH2O] Respiration O2 Mn4+ NO3- N2 Fe3+ SO42- CO2 H2O N2-fixation +CO2 Photosynthesis

  3. The rise of oxygen altered the N cycle- The BIG FLIP • Oxygen permitted NH4 to be converted to NO3 – which can be rapidly reduced to N2. • There was a critical time in Earth’s history when the N cycle was a major barrier to oxidizing the planet • Once over that “hump” we entered a new stable state.

  4. d34S sulfate d34S sulfide D33S Courtesy of Farquhar et al, Science 2004

  5. After Jenkyns et al. (2002)

  6. Similar feedback during Oceanic Anoxic Events? • Anoxic environments: •  denitrification  removal of fixed nitrogen from the ocean • retards of primary production, favors N2-fixers Jenkyns et al. 2001

  7. Quan et al., Global Biogeochem Cycles, in press

  8. Is there evidence in the paleorecord?

  9. Godfrey and Falkowski, in press

  10. Evidence of lateral gene transfer of nif genes Shi and Falkowski, PNAS 2008

  11. O2-mediated Mn -mediated Fe-mediated S-mediated N-mediated H2 or C-mediated Mn2+ NH4+ Fe2+ HS- CH4 H2 [CH2O] Respiration O2 Mn4+ NO3- N2 Fe3+ SO42- CO2 H2O N2-fixation +CO2 Photosynthesis Falkowski, Fenchel and Delong, Science, 2008

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