Variation in δ¹³C and δ¹⁵N within and among plant species in the alpine tundra

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 variations 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 that although 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.