The greenhouse gas, nitrous oxide, is produced in well-aerated soils by two groups of microbes that convert ammonia to nitrite, bacterial ammonia oxidisers (AOB) and archaeal ammonia oxidisers (AOA). Previous studies have shown that nitrous oxide production by AOB increases as oxygen concentration decreases. Thus oxygen appears to affect the pathway in AOB leading to nitrous oxide, which is generated directly by the cells though enzymatic reactions. The effect of oxygen on nitrous oxide production by AOA is less well understood. We assume that AOA produce nitrous oxide only indirectly via chemical reactions of intermediates, that is likely less affected by oxygen concentration. To elucidate this we compared nitrous oxide production by AOA and AOB pure laboratory cultures grown at contrasting initial oxygen concentrations and monitored nitrification kinetics during oxygen depletion. As long as oxygen was available, ammonia was oxidised to nitrite, with AOA possessing a higher affinity for oxygen than AOB. AOB generally produced more nitrous oxide than AOA. Moreover the nitrous oxide production by AOB, but not AOA, increased strongly at very low oxygen concentrations for AOB. The findings reflect the enzymatic versus chemical nitrous oxide production pathways in AOB and AOA, respectively, and open new perspectives for nitrous oxide mitigation strategies.
Published 22. May 2015 - 14:01 - Updated 18. September 2015 - 15:19