Influence of acid rain and liming on fluxes of NO and NO2 from forest soil

Flux measurements of nitric oxide (NO) and nitrogen dioxide (N02) were performed in a coniferous forest (Höglwald) in southern Germany using a fully automated measuring system based on the dynamic chamber method. The forest soil was predominately a source of NO, but mean flux rates of NO ranged from -26.3 (deposition) to 55 my g N m(-2) h(- 1) (emission). NO2 was deposited on the forest soil with mean flux rates ranging from -4 to -72 my g N m(-2) h(-1) . Removal of forest floor vegetation did not influence NO or NO2 fluxes. Apparently, forest floor vegetation was neither a source of NO nor a significant sink of NO2. When the organic layer of the forest soil was removed, net NO flux changed from emission to deposition. Thus NO emitted to the atmosphere was produced almost exclusively in the organic layer of the forest soil. Liming caused a significant decrease in the rate of NO emission by 43 to 100 per cent, whereas irrigation with simulated acid rain increased the emission of NO by a factor of 3. 1. Irrigation with simulated "normal" rain decreased the emission of NO by 35 to 100 per cent. No such effects could be detected for the deposition of NO2.