The relative contribution of ammonia oxidizing bacteria and archaea to N2O emission from two paddy soils with different fertilizer N sources: A microcosm study

Ammonia oxidizing bacteria (AOB) and archaea (AOA) have different affinities to different fertilizer N sources; however, there are few studies on the relative contribution of AOB and AOA to N2O emissions under different N fertilizers. In this study, acetylene (0.01%v/v C2H2) and 1-octyne (0.01%v/v) were used to assess the relative contribution of AOB and AOA to N2O emission from paddy soils with different soil pH and N fertilizers application by incubation in microcosms. The results indicated that cumulative N2O emissions from the alkaline paddy soil were significantly higher than those from the acidic paddy soil, and urea-N application promoted more N2O emissions than ammonium-N application. The total relative contribution of AOA and AOB exceeded 60%, so autotrophic nitrification was the main N2O emission process in both soils at 80% water holding capacity (WHC); after N application, their total contribution increased. The relative contribution of 1-octyne-sensitive AOB (> 45%) to N2O emissions was significantly higher than that of AOA (< 15%) in both tested soils without N application, and its contribution decreased after ammonium-N application in both soils and urea-N application in alkaline soil. The promoting effects of urea-N on N2O yields of AOB were greater than those by ammonium-N; on the contrary, the N2O yields of AOA were more sensitive to ammonium-N application. The main species of nitrifers, Nitrosospira-AOB, Nitrosovibrio-AOB, and Nitrososphaera-AOA, were involved in N2O emissions in both soils.