Increased expression of bacterial amoA during an N2O emission peak in an agricultural field

Abstract Levels of N-cycle gene transcripts ( nirK , nirS , nosZ , amoA ) were measured during an N 2 O emission peak in an agricultural soil. Automated dynamic closed chambers were used to monitor an N 2 O emission peak on a maize crop after a natural rainfall. The peak occurred rapidly after the rainfall began. Spatial and temporal variability in N 2 O emission was observed between chambers. An analysis of N-cycle gene transcript levels revealed an increase in bacterial amoA gene transcripts (but not in archaeal amoA transcripts), correlating strongly with N 2 O emission. This suggests the involvement of nitrification enzymes, despite a high water-filled pore space (80%). Reverse transcription of bacterial 16S rRNA followed by partial sequencing of the resulting cDNAs revealed few rainfall-induced changes in the potentially active bacterial community, and notably no significant change in the relative abundance of 16S rRNAs from the nitrifier genus Nitrosospira . Expression of the amoA gene appears as a possible proxy for monitoring the N 2 O emission peak. To our knowledge, this is the first experiment to evaluate the expression of N-cycle genes during an N 2 O emission peak on an agricultural field.