Long-term behaviour of 15N in an alpine grassland ecosystem

Nitrogen dynamics in semi-natural environments is crucial for the development and ecological stability of these systems. The present paper shows the results of the reinvestigation of a N-15-tracer experiment, which was established in the Grossglockner massif in Austria at 2300 ma. s. l. in 1974/1975. We show that large quantities of nitrogen introduced by a single pulse labelling ( amounting to approximately 1.7% of the nitrogen in the system) into an alpine grassland remain in the soil - plant system, with only 55% being lost during 27 - 28 years. In the first 10 cm of the four investigated soil profiles 40% of N-15 was recovered, being mainly bound in organic forms. A simple site specific model was established on the basis of the results considering a biological, residual and labile N-pool, the latter being the source for N-losses. By the model a long mean residence time close to 100 years was derived for the remaining N-15.