The use of stable isotopes in ecosystem research. First results of a field study with 15N

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Abstract
Terrestrial ecosystems, e.g. forest ecosystems, are characterized by a complex and sensitive network of biotic and abiotic factors and their interactions. By using stable isotopes (e.g. labelled nitrogen compounds), very small addition rates of highly enriched compounds can be applied, which do not change or disturb the investigated system, but provide information about single processes, their interactions and especially about their dynamics. First results of a field study in the Fichtelgebirge, Northeast-Bavaria, Germany, are presented. The distribution of labelled nitrogen (as 15N-NH4 + and 15N[sbnd]NO3 −) within a spruce ecosystem (Picea abies (L.) Karst. in competition with understory vegetation of Vaccinium myrtillus, Calluna vulgaris and Deschampsia flexuosa) showed maximum 15N concentrations in tissues of the understory vegetation. During the first six weeks after the 15N application, the nitrogen uptake of all investigated species was higher after the 15N[sbnd]NO3 − treatment than after the 15N[sbnd]NH4 + treatment.