Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/1993
Publication Date: N/A
Interpretive Summary: There has been an increasing concern over atmospheric pollutants and recently the concern has turned to natural sources of gaseous pollutants. The shrub-steppe ecosystem is a significant land area of North America and other parts of the world. Since this ecosystem is largely undisturbed questions have arisen about it's ability to contribute to atmospheric N2O pools. In addition it is of interest what regulates this N2O production process. We have discovered that the nitrification processes contributes a major portion of the total N2O produced by this ecosystem contrary to the long held belief that denitrification was the source. In addition we have found that the soil wetting history regulates the total N2O produced and that spatial variation needs to be considered when making landscape estimates of N2O fluxes.
Technical Abstract: The semi-arid shrub-steppe os the largest grassland-type ecosystem of North America and may make significant contributions to global atmospheric N2O. Experiments were conducted to determine the relative importance of nitrification, denitrification, and abiotic sources to total N2O flux and to investigate the factors regulating N2O flux rates from an undisturbed shrub-steppe ecosystem. The contributions to N2O flux by nitrification and denitrification were estimated using acetylene (10 Pa) to selectively inhibit N2O production by nitrifiers. Factors limiting N2O production were evaluated by monitoring N2O flux rates from soil-cores amended with combinations of NO3-N, NH4-N, soluble C, and water. The regulating effect of wet-dry cycles on N2O flux was determined by wetting field dry soil to field capacity and monitoring N2O flux rates, soil NH4-N, NO3-N, and water content throughout a drying period. Our results showed that nitrification accounts for 61 to 98% of the N2O produced from soil at water contents below saturation and that denitrification is the primary N2O source at saturated water contents. In intact soil cores N2O flux rates were found to be most limited by water and N availability. Since soil moisture concentration is generally well below field capacity in this ecosystem, nitrification must be the predominant N2O source. These results suggest that conditions favorable for substantial N2O production is shrub-steppe ecosystems probably exist only at times following precipitation events.