Species specific and environment induced variation of δ13C and δ15N in alpine plants

Stable carbon and nitrogen isotope signals in plant tissues integrate plant-environment interactions over long periods. In this study, we hypothesized that humid alpine life conditions are narrowing the scope for significant deviations from common carbon, water and nitrogen relations as captured by stable isotope signals. We explored the variation in δ(13)C and δ(15)N in 32 plant species from tissue type to ecosystem scale across a suite of locations at c. Two thousand five hundred meter elevation in the Swiss Alps. Foliar δ(13)C and δ(15)N varied among species by about 3-4‰ and 7-8‰ respectively. However, there was no overall difference in means of δ(13)C and δ(15)N for species sampled in different plant communities or when bulk plant dry matter harvests of different plant communities were compared. δ(13)C was found to be highly species specific, so that the ranking among species was mostly maintained across 11 habitats. However, δ(15)N varied significantly from place to place in all species (a range of 2.7‰) except in Fabaceae (Trifolium alpinum) and Juncaceae (Luzula lutea). There was also a substantial variation among individuals of the same species collected next to each other. No difference was found in foliar δ(15)N of non-legumes, which were either collected next to or away from the most common legume, T. alpinum. δ(15)N data place Cyperaceae and Juncaceae, just like Fabaceae, in a low discrimination category, well separated from other families. Soil δ(15)N was higher than in plants and increased with soil depth. The results indicate a high functional diversity in alpine plants that is similar to that reported for low elevation plants. We conclude that the surprisingly high variation in δ(13)C and δ(15)N signals in the studied high elevation plants is largely species specific (genetic) and insensitive to obvious environmental cues.