Nitrite-driven nitrous oxide production under aerobic soil conditions: kinetics and biochemical controls

摘要

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 (P-N2O) to NO2- was observed at concentrations below 60 mu gNg(-1) soil in both nonsterile and sterilized soils. Rate coefficients (K-p) 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 (O-2) 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 O-2 levels below 5%. Greater temperature sensitivity was observed for biological compared with 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 O-2. 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.