Soil water controls on aerobic soil emission of gaseous nitrogen oxides
1993
Hutchinson, G.L. | Guenzi, W.D. | Livingston, G.P.
Soil water content has multiple effects on the emission of gaseous N oxides. To separate and characterize these effects, we monitored rates of CO2, NO, and N2O evolution and changes in inorganic N concentrations of soil under a factorial combination of three N treatments and three water treatments during a 10-day laboratory incubation study. Because the emission of NO from control and NH4NO3-amended soil varied with the rate of chemoautotrophic NH4+ oxidation and was virtually eliminated by a specific inhibitor of that process [nitrapyrin (2-chloro-6-(trichloromethyl)-pyridine)], we concluded that nitrification was the principal NO source over the entire tested range of soil water potentials (- 10 to less than - 1000 kPa). Denitrification made no significant contribution to N oxide emissions from even the wettest soil, so nitrifiers were probably also responsible for the much smaller emission of N2O under all treatments. Slower gas diffusion in soil with highest, compared to lowest, water content caused a 3-fold reduction in the mean NO:NO3- product ratio of nitrification, suggesting that the NO produced by NH4+-oxidizers is further oxidized unless conditions permit its rapid escape to the atmosphere. Nitrapyrin also eliminated the brief burst of N oxide emissions that typically follows wetting of dry soil, indicating that chemoautotrophic NH4+ oxidation is also involved in this phenomenon despite the poor correlation of the burst's magnitude with soil NH4+ or NO2- concentrations. A second burst of N oxide emissions from control or NH4NO3-amended soil with no inhibitor occurred only where desiccation reduced both NO and CO2 evolution to near zero prior to rewetting the soil after a 7-day drying cycle.
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