Contribution of nitrification and denitrification sources for seasonal N2O emissions in an acid German forest soil

A 15N tracer field experiment was carried out in an acid soil of a beech forest gap at the Solling area in Germany to determine the different formation processes of N2O. This site has been classified as a seasonal N2O emission type forest. Small amounts of highly enriched 15N tracer were supplied separately as labelled NH4+ and NO3− seven times from May to October 1998. The 15N compounds were injected with syringes into the upper 10 cm of the soil. The N2O emission showed a seasonal pattern with low emission in spring, high emission in summer, and low emission in autumn and followed the soil temperature. N2O was evolved only from the 15N-labelled NO3− pool in summer under field moist conditions, indicating that its formation was due to denitrification. In spring, early summer and autumn trapped N2O or heterotrophic nitrification may also have been involved in N2O emission.