Environmental controls over soil-atmosphere exchange of N2O, NO, and CO2 in a temperate Norway spruce forest

Trace gas exchange of N2O, NO, and CO2 between soil and the atmosphere was measured with high temporal resolution for 5 years (2004-2008) at the Hoglwald Forest, Germany, using a fully automated measuring system. On the basis of these long-term continuous measurements, we calculated the annual budgets of soil-atmosphere trace gas exchange with high accuracy and demonstrated substantial seasonal and interannual variations. The mean annual soil-atmosphere exchange of N2O, NO, and CO2 at our site for the years 2004-2008 was 1.20 +/- 0.09 kg N2O-N ha(-1) yr(-1), 8.64 +/- 0.19 kg NO-N ha(-1) yr(-1), and 7.15 +/- 0.08 t CO2-C ha(-1) yr(-1), respectively. Seasonal patterns of soil N2O fluxes were characterized by event emissions, generally occurring during thawing after longer freezing periods. In contrast to N2O emissions, the seasonal patterns of NO and CO2 soil-atmosphere exchange followed soil temperature changes, although a substantial increase in CO2 emissions was also observed during the freeze and thaw periods. The fact that NO fluxes were higher than N2O emissions during most of the entire observation period indicated that nitrification might have been the primary pathway of N-trace gas production in our study. The extremely high N2O emissions and the substantial interannual variation of N2O flux rates caused by the freeze and thaw effect demonstrate the need for long-term measurements with high temporal resolution in order to come up with more reliable estimates of soil-atmosphere trace fluxes.