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DIVISION S-3-SOIL BIOLOGY & BIOCHEMISTRY

Effects of Oxygen on Denitrification Inhibition, Repression, and Derepression in Soil Columns

^a Dep. of Chemistry and Biochemistry, Univ. of Windsor, Windsor, ON, Canada N9B 3P4
^b Greenhouse and Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, ON, Canada N0R 1G0

Corresponding author (druryc{at}em.agr.ca)

Although it is known that O₂ inhibits and represses denitrification, few studies have examined the effect of O₂ on NO production. Our objectives were to measure O₂ inhibition, repression, and derepression of NO and N₂O production by denitrifying microorganisms in soil columns continuously purged by N₂ or various constant (0.074–15%) O₂–N₂ mixtures. Net rates of NO and N₂O production were measured under successive anaerobic, partially aerobic, and anaerobic conditions. Oxygen inhibition was rapid and reversible. Within 5 min after exposure to >5% O₂, NO production was reduced to 50 to 58% and N₂O rates to 29 to 32% of their maximum anaerobic rates. Maintaining O₂ at 5% in soil without added C or at >10% O₂ in C-amended soil decreased (repressed) NO production rates by a factor of 1.5 to 1.8 d^-1. Rates of N₂O repression remained constant at 0.07 d^-1 for all C and O₂ treatments. Restoration of anoxic conditions following the aerobic phase reversed inhibition; within 5 min, NO production rates by the nonrepressed denitrifiers increased to 55 to 101% of their respective anaerobic rates and N₂O production rates increased to 26 to 62%. The rates of NO and N₂O production then increased more slowly (derepression) during this anaerobic period. This research supports previous observations for O₂ effects on N₂O production and apparently is the first systematic study of O₂ inhibition, repression, and derepression of NO production.