Rapid nitrate reduction produces pulsed NO and N2O emissions following wetting of dryland soils

Soil drying and wetting cycles can produce pulses of nitric oxide (NO) and nitrous oxide (N2O) emissions with substantial effects on both regional air quality and Earth’s climate. While pulsed production of N emissions is ubiquitous across ecosystems, the processes governing pulse magnitude and timing remain unclear. We studied the processes producing pulsed NO and N2O emissions at two contrasting drylands, desert and chaparral, where despite the hot and dry conditions known to limit biological processes, some of the highest NO and N2O flux rates have been measured. We measured N2O and NO emissions every 30 minutes for 24 hours after wetting soils with isotopically-enriched nitrate and ammonium solutions to determine production pathways. Nitrate was reduced to N2O within 15 minutes of wetting, with emissions exceeding 1000 ng N-N2O m-2 s-1 and returning to background levels within four hours, but the pulse magnitude did not increase in proportion to the amount of ammonium or nitrate add...