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Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/19/2007 Publication Date: 7/1/2007 Citation: Venterea, R.T. 2007. Nitrite-driven nitrous oxide production under aerobic soil conditions: Kinetics and biochemical controls. Global Change Biology. 13:1798-1809. Interpretive Summary: Denitrification under anaerobic conditions is commonly considered to be the primary source of nitrous oxide (N2O) in fertilized soil, but much less is known about N2O produced under aerobic conditions. This study investigated N2O production via biological and chemical reactions occurring in the presence of oxygen (O2) and nitrite (NO2-), which commonly accumulates following fertilizer application. Model simulations using the measured kinetic rate coefficients predicted that N2O generated in aerobic soil can be comparable to, or greater than, fluxes generated via denitrification. Rate coefficients varied over two orders of magnitude and were strongly correlated (r2=0.84) with soil organic carbon (C), suggesting that agricultural management practices designed to increase soil C storage may have unintended consequences that could counteract greenhouse gas benefits. Abiotic processes, which are promoted at lower pH, accounted for 31–75% of total N2O production, indicating that pH management may be effective in mitigating total N2O missions. Biological reduction of NO2- was enhanced as O2 levels were decreased from above ambient to 5%, while nitrate (NO3-)-reduction and the reduction of N2O itself were only stimulated at O2 levels below 5%. Thus, understanding controls over N2O production under field conditions is complicated by the potential presence of several microbial and chemical production processes that are difficult to distinguish without detailed measurements. These results have implications with regard to improved management to minimize agricultural N2O emissions and improved emissions assessments. Technical Abstract: Nitrite (NO2-) can accumulate during nitrification in soil following fertilizer application. While the role of NO2- as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil-to-atmosphere fluxes as a function of NO2- levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N2O production rate (PN2O) to NO2- was observed at concentrations below 60 ug N g-1 soil in both non-sterile and sterilized soils. Rate coefficients (Kp) relating PN2O to NO2- varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in Kp across all samples. Abiotic processes accounted for 31–75% of total N2O production. Biological reduction of NO2- was enhanced as oxygen (O2) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO3-)-reduction, and the reduction of N2O itself, were only stimulated at O2 levels below 5%. Greater temperature sensitivity was observed for biological compared to chemical N2O production. Steady-state model simulations predict that NO2- levels often found after fertilizer applications have the potential to generate substantial N2O fluxes even at ambient O2. This potential derives in part from the production of N2O under conditions not favorable for N2O reduction, in contrast to N2O generated from NO3- reduction. These results have implications with regard to improved management to minimize agricultural N2O emissions and improved emissions assessments. |
