Archaea May Be Key Nitrous Oxide Source

The large quantities of the ozone-destroying greenhouse gas nitrous oxide (N₂O) released from Earth’s oceans into the atmosphere may be generated by single-celled archaea, rather than bacteria, scientists report (Science, DOI: 10.1126/science.1208239). Although oceanic bacteria had been thought to produce most of Earth’s marine N₂O via oxidation of ammonia and reduction of nitrogen oxides, that idea never jibed with isotopic N₂O studies that compared the microbially produced gas with N₂O in the atmosphere. Karen L. Casciotti and Alyson E. Santoro of Woods Hole Oceanographic Institution and their colleagues now show that cultures of marine archaea produce N₂O via ammonia oxidation. In addition, they found that the isotope ratios of oxygen and nitrogen in the archaea-produced N₂O and in atmospheric N₂O contributed by the ocean are similar. The results “suggest that ammonia-oxidizing archaea likely play an important role in N₂O production in the near-surface ocean,” the researchers write.