Relationships between ammonia oxidizers and N2O and CH4 fluxes in agricultural fields with different soil types

Nitrous oxide (N2O) is a greenhouse gas that contributes to the destruction of stratospheric ozone, and agricultural soil is an important source of N2O. Aerobic soils are sinks for atmospheric methane (CH4), a greenhouse gas. Ammonia monooxygenase (AMO) can oxidize CH4, but CH4 is mostly oxidized by methane monooxygenase (MMO), and CH4 oxidation by AMO is generally negligible in the soil. We monitored the N2O and CH4 fluxes after urea application in fields containing different soils using an automated sampling system to determine the effects of environmental and microbial factors on the N2O and CH4 fluxes. The soil types were Low-humic Andosol (Gleyic Haplic Andosol), yellow soil (Gleyic Haplic Alisol) and gray lowland soil (Entric Fluvisol). Cumulative N2O emissions from the yellow soil were higher than those from other soil types, although the difference was not significant. The CH4 uptake level by Andosol was one order of magnitude higher than that by other soils. There were significant relationships between the ammonia oxidation potential, AOB and AOA amoA copy numbers, and the CH4 uptake. In contrast, the gene copy numbers of methane-oxidizing bacteria (MOB) pmoA were below the detection limit. Our results suggested that the AMOs of AOB and AOA may have more important roles than those previously considered during CH4 oxidation in agricultural soils treated with N fertilizers.