Marko J. Spasojevic, Sören Weber1

Ratios of carbon (C) and nitrogen (N) stable isotopes in plants are important indicators of intrinsic water use efficiency and N acquisition strategies. Here, we examined patterns of inter- and intraspecific variation and phylogenetic signal in foliar δ13C and δ15N for 59 alpine tundra plant species, stratifying our sampling across five habitat types. Overall, we found that variation in both δ13C and δ15N mirrored well-known patterns of water and nitrogen limitation among habitat types and that there was significant intraspecific trait variation in both δ13C and δ15N for some species. Lastly, we only found a strong signal of phylogenetic conservatism in δ13C in two habitat types and no phylogenetic signal in δ15N. Our results suggest while local environmental conditions do play a role in determining variation in δ13C and δ15N among habitat types, there is considerable variation within and among species that is only weakly explained by shared ancestry. Taken together our results suggest that considering local environmental variation, intraspecific trait variation, and shared ancestry can help with interpreting isotope patterns in nature and with predicting which species may be able to respond to rapidly changing environmental conditions.