DENITRIFICATION IN SEVERAL ALBERTA SOILS: INHIBITION BY SULFUR ANIONS

Abstract

The microbial potential for denitrification and the effects of sulfur anions on this process were assessed in five Alberta soils. The denitrification potential of the various soils was ranked as follows: Black > Dark Brown > Brown [Formula: see text] Gray Luvisol [Formula: see text] Solodized Solonetz. The rate of denitrification in any soil was dependent on the chemical characteristics of that soil and the availability of a suitable carbon substrate for the denitrifying microorganisms. Denitrification was stimulated in three of the last four soils by adding 300 μg glucose-C/g of soil. Addition of 100 or 500 μg SO42−-S/g of soil had little or no effect on the rate of denitrification. In contrast, soils with added Na2SO3, Na2S2O3, and Na2S had reduced rates of denitrification and nitrite accumulated. The data suggest that microbial reduction of these sulfur anions to S2− occurred, and that S2− blocked the terminal steps of the enzyme pathway for denitrification, resulting in the accumulation of NO2−. The inhibition of denitrification by the sulfur anions could be overcome by adding 900 μg glucose-C/g of soil.