Shift in soil-plant nitrogen dynamics of an alpine-nival ecotone

We investigated the nitrogen (N) dynamics of an alpine-nival ecotone on Mt. Schrankogel, Tyrol, Austria, in relation to temperature. Natural abundance of N-15 was used as a tool to elucidate differences in N cycling along an altitudinal transect ranging from 2,906 to 3,079 m, corresponding to a gradient in mean annual temperature of 2.4 degrees C. The amount of total soil N, of plant available N and soil C/N ratio decreased significantly with increasing altitude, whereas soil pH increased. Soil delta N-15 decreased with increasing altitude from +2.2 to -2.1 parts per thousand and delta N-15 of plant tissues (roots and leaves) decreased from -3.7 to -5.5 parts per thousand. The large shift in soil delta N-15 of 4.3 parts per thousand from the lowest to the highest site suggested substantial differences in N cycling in alpine and nival ecosystems in the alpine nival ecotone investigated. We concluded that N cycling at the alpine-nival ecotone is likely to be controlled by various factors: temperature, soil age and development, atmospheric N deposition and plant competition. Our results furthermore demonstrate that the alpine-nival ecotone may serve as a sensitive indicator of global change.