Effects of sulfide and acetylene on nitrous oxide reduction by soil and by Pseudomonas aeruginosa

Abstract

The production and reduction of nitrous oxide (N₂O) after the addition of N₂O, nitrite (NO₂⁻), or nitrate (NO₃⁻) was studied in non-sterile soil, in sterilized soil inoculated with Pseudomonas aeruginosa, and in washed cell suspensions of this organism. Sodium sulfide (8 μmol S²⁻ mL⁻¹ or g⁻¹) inhibited N₂O reduction markedly in cell suspensions and also in soil, an effect which may cause sulfidic habitats to act as sources of N₂O. Sodium thiosulfate (up to 64 μmol S₂O₃²⁻ g⁻¹) showed no such effect. Acetylene (0.02 atm C₂H₂) completely inhibited the reduction of N₂O by soil, but the combination of C₂H₂ with 8 μmol S²⁻ g⁻¹ permitted the complete reduction of 2 μmol added N₂O g⁻¹ within 3 days under the most favourable conditions. Under the same conditions, 8 μmol S₂O₃²⁻ g⁻¹ permitted complete reduction of the N₂O within 6 days. The rate of such reduction of N₂O was decreased, but not inhibited completely, by raising the C₂H₂ concentration to 0.11 atm. The data have important implications for the effectiveness of the C₂H₂ inhibition assay of denitrification in highly anaerobic environments.