Soil N₂O and NO emissions from an arid, urban ecosystem

We measured soil nitrogen (N) cycling and fluxes of N₂O and NO in three land-use types across the metropolitan area of Phoenix, Arizona. Urbanization increased N₂O emissions compared to native landscapes, primarily due to the expansion of fertilized and irrigated lawns. Fluxes of N₂O from lawns ranged from 18 to 80 μg N 2 m^-2 h^-1 and were significantly larger than managed xeric landscapes (2.5-22 μg N m^-2 h^-1) and remnant desert sites within the urban core (3.7-14 μg N m^-2 h^-1). In contrast, average NO fluxes from 2 lawns were not significantV different from native desert when dry (6-80 μg N m^-2 h^-1 lawn; 5-16 μg N m^-2 h^-1 desert) and were lower than fluxes from deserts after wetting events. Furthermore, urbanization has significantly altered the temporal dynamics of NO emissions by replacing pulse-driven desert ecosystems with year-round irrigated, managed lawns. Short-term, pulse-driven emissions of NO from wetting of dry desert soils may reach 35% of anthropogenic emissions within a day after summer monsoon storms. If regional O₃ production is NO_x-limited during the monsoon season, fluxes from warm, recently wet arid soils may contribute to summer O₃ episodes.