Nitrogen fertiliser-induced changes in N2O emissions are attributed more to ammonia-oxidising bacteria rather than archaea as revealed using 1-octyne and acetylene inhibitors in two arable soils

Abstract

Nitrification is believed to be one of the major sources of N2O production emitted from soil. Previous studies showed that both ammonia-oxidising bacteria (AOB) and archaea (AOA) can produce N2O via nitrification but their relative contributions are still poorly defined. Here, we used acetylene, an inhibitor of AOB and AOA ammonia monooxygenase (AMO), and 1-octyne, a selective inhibitor that specifically inhibits AOB AMO, to investigate how AOB versus AOA contribute to N2O emissions in two distinct arable soils. Soil amended with ammonium (NH4 +) increased N2O emissions to a greater extent than nitrate (NO3 −), and acetylene had a greater impact on N2O emissions in NH4 +-treated soils than that in NO3 −-amended soils, which indicated that nitrification was the dominant N2O emitting process in these two arable soils. In the alluvial and red soil, the percentage of evolved N2O after application of NH4 + by AOB were 70.5 ~ 78.1 % and 18.7 ~ 19.7 % by AOA, respectively. Quantitative PCR revealed that NH4 + addition stimulated AOB growth, and the growth could be significantly inhibited by acetylene or 1-octyne in the two soils. The stimulation of N2O emissions by NH4 + and the relative suppression by inhibitors paralleled fluctuations in the AOB growth. In addition, cumulative N2O emissions were not correlated with AOA abundance in the two soils. Our results revealed that AOB could contribute more to soil N2O production than AOA in the NH4 +-amended arable soils.