DENITRIFICATION AND GASEOUS NITROGEN LOSSES FROM AN ACID SPRUCE FOREST SOIL

To quantify gaseous N-emissions in an approximately 80-y-old spruce fo rest, in-situ measurements were carried out every 2 wk over one year. Using the acetylene inhibition technique, soil cores (0-10 cm) were in cubated for 24 h under 10 kPa acetylene to detect (N-2 + N2O)-N from d enitrification. Additional soil cores were incubated without C2H2 to m easure the overall;N2O-N emission (derived from denitrification and ni trification). The site receives an N-input of:approximately 11.5 kg N ha(-1) y(-1) through wet deposition. On an annual basis, N2O emissions from this forest soil were calculated to be 81 g N ha(-1) y(-1), wher eas N-losses from both denitrification and nitrification were lower th an 176 g ha(-1) y(-1): Low net nitrification may be the main reason fo r the low N2O and N-2 emission. Gaseous N-losses showed a slight seaso nal trend as emissions were lowest during the winter season (December- March), whereas highest values were measured in spring (under 10 kPa C 2H2) Or early summer (without C2H2) The highest denitrification rate o ccurred when the NO3--content was high in the OfOh-horizon, indicating that the denitrifying activity may rise significantly if a critical N d-3(-)-concentration is reached. NO3 was also shown to limit denitrifi cation under laboratory conditions using intact soil cores. (C) 1997 E lsevier Science Ltd.