PRJNA283253
Diversity of the N2O reducers matters for the relative proportion of N2O emitted by denitrification across cropping systems.
Agriculture is the main source of terrestrial emissions of N2O, the third major greenhouse gas and the main depleting substance of the ozone layer. The reduction of N2O into N2 by microorganisms carrying the nitrous oxide reductase (NosZ) is the unique biological process known to eliminate this greenhouse gas. Recent studies revealed that a new clade of N2O reducing microorganisms was related to the soil N2O sink capacity, opening the way for new strategies to mitigate N2O emissions. Here, we investigated whether the agricultural practices could differently influence the abundance and the diversity of the two clades of N2O reducers with consequences for the denitrification end product ratio. The abundance of N2O-reducers and producers was quantified by real-time PCR, and the diversity of both nosZ clades was determined by 454 pyrosequencing. To characterize the activity of denitrifying microbial communities, potential N2O emissions, the potential denitrification activity (PDA) and the proportion of N2O emitted [rN2O/r(N2O+N2)] were calculated. Altogether, our results showed limited differences driven by individual agricultural practices but contrasting  cropping systems showed significant differences in both the abundance and structure of the nosZII community, as well as in the proportion of N2O emitted by denitrification. In contrast, more limited differences were observed in the nosZI community, which suggests that the newly identified nosZII clade is more sensitive than nosZI to environmental changes. Accordingly, shared but also distinct soil properties were related to variations in the nosZI and nosZII community structure. Noteworthy, while PDA and potential N2O emissions were mostly explained by the soil properties, diversity of the nosZII clade alone explained 26% of the proportion of N2O emitted, strengthening the importance of understanding the ecology of this new clade of N2O reducing microorganisms for mitigation strategies.