IMS-7:

Nitrous oxide production by soil ammonia-oxidizing Thaumarchaeota

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