The Influence of Atmospheric N Deposition on Nitrous Oxide and Nitric Oxide Fluxes and Soil Ammonium and Nitrate Concentrations

Abstract

The deposition of atmospheric N to soils provides sources of available N to the nitrifying and denitrifying microbial community and subsequently influences the rate of NO and N2O emissions from soil. We have investigated the influence of three different sources of enhanced N deposition on NO and N2O emissions 1) elevated NH3 deposition to woodlands downwind of poultry and pig farms, 2) increased wet cloud and occult N deposition to upland forest and moorland and 3) enhanced N deposition to trees as NO-3 and NH+4 aerosol. Flux measurements of NO and N2O were made using static chambers in the field or intact and repacked soil cores in the laboratory and determination of N2O by gas chromatography and of NO by chemiluminescence analysis. Rates of N deposition to our study sites were derived from modelled estimates of N deposition, NH3 concentrations measured by passive diffusion and inference from measurements of the 210Pb inventory of soils under tree canopies compared with open grassland. NO and N2O emissions and KCl-extractable soil NH+4 and NO-3 concentrations all increased with increasing N deposition rate. The extent of increase did not appear to be influenced by the chemical form of the N deposited. Systems dominated by dry-deposited NH3 downwind of intensive livestock farms or wet-deposited NH+4and NO-3 in the upland regions of Britain resulted in approximately the same linear response. Emissions of NO and N2O from these soils increased with both N deposition and KCl extractable NH+4, but the relationship between NH+4 and N deposition (ln NH+4 = 0.62 ln Ndeposition+0.21, r2 = 0.33, n = 43) was more robust than the relationship between N deposition and soil NO and N2O fluxes