Effects of sulfide and acetylene on nitrous oxide reduction by soil and by <i>Pseudomonas aeruginosa</i>

Abstract

The production and reduction of nitrous oxide (N 2 O) after the addition of N 2 O, nitrite (NO 2 − ), or nitrate (NO 3 − ) 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 S 2− mL −1 or g −1 ) inhibited N 2 O reduction markedly in cell suspensions and also in soil, an effect which may cause sulfidic habitats to act as sources of N 2 O. Sodium thiosulfate (up to 64 μmol S 2 O 3 2− g −1 ) showed no such effect. Acetylene (0.02 atm C 2 H 2 ) completely inhibited the reduction of N 2 O by soil, but the combination of C 2 H 2 with 8 μmol S 2− g −1 permitted the complete reduction of 2 μmol added N 2 O g −1 within 3 days under the most favourable conditions. Under the same conditions, 8 μmol S 2 O 3 2− g −1 permitted complete reduction of the N 2 O within 6 days. The rate of such reduction of N 2 O was decreased, but not inhibited completely, by raising the C 2 H 2 concentration to 0.11 atm. The data have important implications for the effectiveness of the C 2 H 2 inhibition assay of denitrification in highly anaerobic environments.