Isotopic evidence of the effects of herbivory and landscape position on plant nitrogen sources in a riparian ecosystem

摘要

This study used ~(15) N natural abundance techniques to investigate whether elk herbivory affects the capability of willow (Salix spp.) and reed-grass (Carex spp.) to access N from groundwater in upper and lower landscape positions within riparian areas of the Rocky Mountain National Park. For this, δ~(15)N values of plant, soil, rainfall and groundwater samples were measured within a replicated field experiment. Despite the relatively high variability in the ~(15)N data, it provided evidence of the effects of grazing and lanscape position on plant N sources. Carex seemed to acquire less groundwater N in upper landscape positions compared to Salix, maybe due to the deeper willow rooting system. However, grazed willows in upper landscape positions seemed to acquire less groundwater N as compared to willows protected from herbivory. These findings were in accordance with other isotopic and non-isotopic studies conducted in the same experimental site.