Biological oxidation of nitric oxide in a humisol

Abstract

Consumption of nitric oxide (NO) in a humisol was studied at 0.1–2 ppmv NO, a range representative of NO concentrations in ammonium-fertilized soil. Denitrification was not a major sink for NO. The principal NO-consuming reaction was a biological oxidation, leading ultimately to nitrate (NO₃ ^–). Nitrogen dioxide (NO₂) and nitrite (NO₂ ^–) may have been intermediates in this pathway. An abiological reaction accounted for about 25% of the NO-consuming activity in soil at 90% H₂O (d.w.) and 25^oC, but contributed relatively more to total NO consumption at higher temperatures. Biological NO-consuming activity was highest at 25^oC, while the abiological activity increased exponentially with temperature. The product of the abiological reaction was neither NO₃ ^–, NO₂ ^–, nor nitrous oxide (N₂O), and the reaction did not require O₂.