Trace amounts of O sub(2) affect NO and N sub(2)O production during denitrifying enzyme activity (DEA) assays

• Published in: Soil biology & biochemistry 2004-03, Vol.36 (3), p.513-517
• Main Authors: Murray, R E, Knowles, R
• Format: Article
• Language: English
• ISSN: 0038-0717
• DOI: 10.1016/j.soilbio.2003.10.027

We evaluated the potential of trace amounts of O sub(2) inadvertently introduced into anaerobic incubations to initiate the C sub(2)H sub(2)-catalyzed NO oxidation reaction and affect NO and N sub(2)O production rates during denitrifying enzyme activity (DEA) assays. We measured the rate of NO production in the presence and absence of 10 kPa C sub(2)H sub(2) and N sub(2)O production in the presence of 10 kPa C sub(2)H sub(2) by short-term incubations of slurries of humisol and sandy loam soil. NO production, in the absence of C sub(2)H sub(2), was similar for both soils (0.73-1.32 ng NO-N g dry soil super(-1) min super(-1)) and replicate measurements of NO production rates were linear and exhibited small standard deviations. It was not possible to consistently measure NO production in the presence of C sub(2)H sub(2). Replicate measurements of NO production were always lower and exhibited a wide range of variability when C sub(2)H sub(2) was present. The rate of NO production in the absence of C sub(2)H sub(2) was only 2.3-3.0% of the rate of N sub(2)O production in the presence of C sub(2)H sub(2) in humisol soil but was much larger (31.8-35.0%) in the sandy loam soil. Rates of NO production from sandy loam soil were reduced by 58% when trace amounts (30 mu l) of O sub(2) were added to slurry incubations containing C sub(2)H sub(2). We conclude that trace amounts of O sub(2) inadvertently introduced into the slurries during sampling could initiate scavenging of NO by the C sub(2)H sub(2)-catalyzed NO oxidation reaction and cause an underestimate of N sub(2)O production during DEA assays in some soils.