Fluxes of NO and N2O from temperate forest soils. Impact of forest type, N deposition and of liming on the NO and N2O emissions

Annual cycles of NO, NO2 and N2O emission rates from soil were determined with high temporal resolution at a spruce (control and limed plot) and beech forest site ("Höglwald") in Southern Germany (Bavaria) by use of fully automated measuring systems. The fully automated measuring system used for the determination of NO and NO2 flux rates is described in detail. In addition, NO, NO2 and N2O emission rates from soils of different pine forest ecosystems of Northeastern Germany (Brandenburg) were determined during 2 measuring campaigns in 1995. Mean monthly NO and N2O emission rates (July 1994-June 1995) of the untreated spruce plot at the Höglwald site were in the range of 20-130 my g NO-N m(-2) h(-1) and 3.5-16.4 my g N2O-N m(-2) h(-1), respectively. Generally, NO emission exceeded N2O emission. Liming of a spruce plot resulted in a reduction of NO emission rates (monthly means: 15-140 my g NO-N m(-2) h(-1)) by 25-30 per cent as compared to the control spruce plot. On the other hand, lim ing of a spruce plot significantly enhanced over the entire observation period N2O emission rates (monthly means: 6.2-22.1 my g N2O-N m(-2) h(-1)). Contrary to the spruce stand, mean monthly N2O emission rates from soil of the beech plot (range: 7.9-102 my g N2O-N m(-2) h(-1)) were generally significantly higher than NO emission rates (range: 6.1-47.0 my g NO-N m(-2) h(-1)). Results obtained from measuring campaigns in three different pine forest ecosystems revealed mean N2O emission rates between 6.0 and 53.0 my g N2O-N m(- 2) h(-1) and mean NO emission rates between 2.6 and 3 1.1 my g NO-N m(-2) h(-1). The NO and N2O flux rates reported here for the different measuring sites are high compared to other reported fluxes from temperate forests. Ratios of NO/N2O emission rates were > > 1 for the spruce control and limed plot of the Höglwald site and << 1 for the beech plot. The pine forest ecosystems showed ratios of NO/N2O emission rates of 0.9 ¤ 0.4. These results indicate a strong diff erentiating impact of tree species on the ratio of NO to N2O emitted from soil.