Formation of hybrid N₂O in a suspended soil due to co‐denitrification of NH₂OH

A few studies have shown that amine compounds ( e.g., hydroxylamine) can be co‐metabolically introduced into the reaction pathway of denitrification. During this microbial process, the N atom of the amine species is bound to a N atom of nitrite. In case of hydroxylamine, this concomitant reaction ultimately results in the formation of hybrid N 2 O. Due to its co‐metabolic character the process has been termed co‐denitrification. Hybrid N 2 O production during co‐denitrification has been proven to occur in prokaryotic ( e.g., Pseudomonas sp. ) as well as eukaryotic ( e.g., Fusarium sp. ) species. Many of them are already well‐known as common denitrifiers. However, until now no clear evidence has been provided to show that N 2 O production by co‐denitrification really takes place in a soil. In the present study, a formation of hybrid N 2 O was revealed by an adapted 15 N‐tracer model, when both hydroxylamine and 15 N‐nitrate were applied (mol ratio 10:1) to an anaerobically incubated soil suspension from a Haplic Chernozem. The presence of hybrid N 2 O was also indicated by a novel characteristic factor ( R binom ) developed for a hybrid‐N‐N‐gas detection. By contrast, no hybrid N 2 O was found when either an autoclaved soil suspension, only nitrate or only hydroxylamine was used. Thus, it appears that hybrid‐N 2 O formation occurred due to co‐denitrification of hydroxylamine. Hence, this is the first study which demonstrates hybrid‐N 2 O production by co‐denitrification beyond a microbial species level. The 15 N‐tracer model revealed that under the given experimental conditions N 2 O production by co‐denitrification prevailed against N 2 O from denitrification and abiotic hydroxylamine decomposition. In addition, a formation of hybrid N 2 was also calculated by the model. However, the experimental results lead to the conclusion that it was most likely caused by a reduction of hybrid N 2 O due to conventional denitrification.