The contributions of ammonia oxidizing bacteria and archaea to nitrification-dependent N 2 O emission in alkaline and neutral purple soils

Nitrification is believed to be one of the primary processes of N 2 O emission in the agroecological system, which is controlled by soil microbes and mainly regulated by soil pH, oxygen content and NH 4 + availability. Previous studies have proved that the relative contributions of ammonia oxidizing bacteria (AOB) and archaea (AOA) to N 2 O production were varied with soil pH, however, there is still no consensus on the regulating mechanism of nitrification-derived N 2 O production by soil pH. In this study, 1-octyne (a selective inhibitor of AOB) and acetylene (an inhibitor of AOB and AOA) were used in a microcosm incubation experiment to differentiate the relative contribution of AOA and AOB to N 2 O emissions in a neutral (pH = 6.75) and an alkaline (pH = 8.35) soils. We found that the amendment of ammonium (NH 4 + ) observably stimulated the production of both AOA and AOB-related N 2 O and increased the ammonia monooxygenase (AMO) gene abundances of AOA and AOB in the two test soils. Among which, AOB dominated the process of ammonia oxidation in the alkaline soil, contributing 70.8% of N 2 O production derived from nitrification. By contrast, the contribution of AOA and AOB accounted for about one-third of nitrification-related N 2 O in acidic soil, respectively. The results indicated that pH was a key factor to change abundance and activity of AOA and AOB, which led to the differentiation of derivation of N 2 O production in purple soils. We speculate that both NH 4 + content and soil pH mediated specialization of ammonia-oxidizing microorganisms together; and both specialization results and N 2 O yield led to the different N 2 O emission characteristics in purple soils. These results may help inform the development of N 2 O reduction strategies in the future.