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, NO$_{2}$ and N$_{2}$O 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 NO$_{2}$ flux rates is described in detail. In addition, NO, NO$_{2}$ and N$_{2}$O 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 N$_{2}$O emission rates (July 1994–June 1995) of the untreated spruce plot at the Höglwald site were in the range of 20–130 $\mu$g NO-N m$^{-2}$ h$^{-1}$ and 3.5–16.4 $\mu$g N2O-N m$^{-2}$ h$^{-1}$, respectively. Generally, NO emission exceeded N$_{2}$O emission. Liming of a spruce plot resulted in a reduction of NO emission rates (monthly means: 15–140 $\mu$g NO-N m$^{-2}$ h$^{-1}$) by 25-30% as compared to the control spruce plot. On the other hand, liming of a spruce plot significantly enhanced over the entire observation period N$_{2}$O emission rates (monthly means: 6.2–22.1 $\mu$g N$_{2}$O-N m$^{-2}$ h$^{-1}$). ... mehrContrary to the spruce stand, mean monthly N$_{2}$O emission rates from soil of the beech plot (range: 7.9–102 $\mu$g N$_{2}$O-N m$^{-2}$ h$^{-1}$) were generally significantly higher than NO emission rates (range: 6.1–47.0 $\mu$g NO-N m$^{-2}$ h$^{-1}$). Results obtained from measuring campaigns in three different pine forest ecosystems revealed mean N$_{2}$O emission rates between 6.0 and 53.0 $\mu$g N$_{2}$O-N m$^{-2}$ h$^{-1}$ and mean NO emission rates between 2.6 and 31.1 $\mu$g NO-N m$^{-2}$ h$^{-1}$. The NO and N$_{2}$O flux rates reported here for the different measuring sites are high compared to other reported fluxes from temperate forests. Ratios of NO/N$_{2}$O 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/N$_{2}$O emission rates of 0.9 ± 0.4. These results indicate a strong differentiating impact of tree species on the ratio of NO to N$_{2}$O emitted from soil.