Atmospheric nitrous oxide (N2O) gas is involved in global warming and ozone depletion. The major sources of N2O are generally attributed to the activity of nitrifying and denitrifying bacteria. Ammonia-oxidizing archaea (AOA) are major members of the soil ammonia-oxidizing microorganisms. However, the contribution of AOA to N2O production from soil and its mechanism is still unclear. In this study, we investigated the isotopic signatures of N2O produced by soil AOA and its association with N2O production processes. All AOA strains of Thaumarchaeota clades from soils produced N2O and their yields were comparable to those of ammonia-oxidizing bacteria (AOB). The AOA strains shown to produce high amount of N2O by nitrification process, due to its positive site preference value at the end of ammonia oxidation. However, a 15N-labeling experiment indicated that N2O originated from two different production pathways (ammonia oxidation and nitrifier denitrification), which suggests that the isotopic signatures of N2O from AOA may be attributable to the relative contributions of these two processes. Furthermore, to test the how soil acidification affects the N2O production, we studied the isotopic signatures of N2O under various pH conditions. The results show that archaea may contribute to N2O production in terrestrial ecosystems; however, it was not possible to discern N2O from soil AOA because of similarities between its isotopic signatures and those from AOB.
keywords:nitrous oxide,global warming and ozone depletion,Ammonia-oxidizing archaea,isotopic signatures,soil acidification