The δ 18O value of nitrite produced from ammonia oxidation varied with the δ 18O value of water in the medium but was lower than the isotopic equilibrium value in water. We first report the isotope effects of ammonia oxidation at 70☌ by thermophilic Thaumarchaeota populations composed almost entirely of “ Candidatus Nitrosocaldus.” The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. Nitrogen and oxygen isotope ratios of nitrite (δ 15N NO2− and δ 18O NO2−, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature.
0 Comments
Leave a Reply. |