Novel Mechanism of Abiotic Ammonium Oxidation Triggers Nitrous Oxide Bursts Upon Soil Rewetting

Alexander Zherebker, Edwige Demangeat, Isaac Yagle, Mathieu Pédrot, Michael Dannenmann, Nolenn Kermeur, Rémi Marsac, Laura Fablet, Francisco Cabello-Hurtado, Clemens Scheer, Vasily I. Grabovskiy, Ilya Gelfand

Drought-rewetting cycles (DWC) in soil are accompanied by a rapid burst of nitrous oxide (N2O) emission within minutes without reactivation of dormant microbes. Here we present a manifold of evidence for a previously unrecognized abiotic mechanism connecting soil ammonium (NH4+) to N2O with hydroxylamine (NH2OH) as a key intermediate. DWC experiments in the Negev Desert soil revealed comparable short N2O pulses in both live and radiation-sterilised soils. N2O emission increased in a dose-dependent manner following NH2OH addition, underscoring NH2OH availability as a key factor of the observed N2O spikes. Finally, isotope labelling experiments showed that NH4+ directly contributes to N2O emission even in sterilised soil. This pathway is likely facilitated by the extracellular ammonia monooxygenase (AMO) – the only known catalyser of NH4+-NH2OH conversion in soil. Our finding of an additional source of atmospheric N2O extend beyond drylands since abiotic processes and DWC are projected to intensify globally including temperate ecosystems.