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

Levels of N-cycle gene transcripts (nirK, nirS, nosZ, amoA) were measured during an N2O emission peak in an agricultural soil. Automated dynamic closed chambers were used to monitor an N2O emission peak on a maize crop after a natural rainfall. The peak occurred rapidly after the rainfall began. Spatial and temporal variability in N2O 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 N2O 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 N2O emission peak. To our knowledge, this is the first experiment to evaluate the expression of N-cycle genes during an N2O emission peak on an agricultural field.