Contribution of N-15-labelled leaf litter to N turnover, nitrous oxide emissions and N sequestration in a beech forest during eleven years

Decomposition of leaf litterfall plays a major role for nitrogen (N) dynamics in soils. However, little is known as to which extent beech leaf litter contributes to N turnover and nitrous oxide (N2O) emissions within one decade after litterfall. In 1997, we exchanged recently fallen leaf litter by N-15-labelled litter in a beech stand (Fagus sylvatica) at the Solling, Germany. Measurements were conducted 2-3 and 10-11 years after litter exchange. Two years after litter exchange, 92 % of added N-15 was recovered in the surface 10 cm of the soil. The labelled N was primarily found in the upper part of the F layer of the moder type humus. Eleven years after litter exchange, 73 % of the added N-15 was lost and the remaining 27 % was mainly recovered in the lower part of the F layer indicating N sequestration. The remaining leaf litter N was subject to measurable N mineralisation (2-3 % of litter N) and N2O production (0.02 %). Between 0.3 % (eleventh year) and 0.6 % (second year) of total annual N2O emissions were attributed to beech leaf litter of a single year. Most of the annual N2O emissions (1.33-1.54 kg N ha(-1) yr(-1)) were probably derived from older soil N pools.