Variation in n-alkane δD values from terrestrial plants at high latitude: Implications for paleoclimate reconstruction

The molecular hydrogen isotope composition (δD) of leaf waxes from terrestrial plants is increasingly used to infer hydrological characteristics of ancient high latitude climates. Analysis of the hydrogen isotope composition of n-alkanes (δD_n-alkane) from a global dataset of individual plants growing at low and middle latitudes indicates that plant ecological life form is an important factor in determining the hydrogen isotope fractionation. However, environmental and biological controls of high latitudinal leaf wax δD values are poorly understood because of a lack of δD records from modern flora in these regions. We previously noticed smaller apparent hydrogen isotope fractionations between n-alkanes and environmental water (ε_alk-water) in deciduous trees growing at high latitudes (>59°N; Liu, W.-G., Yang, H., 2008. Multiple controls for the variability of hydrogen isotopic compositions in higher plant n-alkanes from modern ecosystems. Global Change Biology 14, 2166-2177.) To further examine these issues, we measured δD_n-alkane from a variety of plants that inhabit high latitude environments and added critically needed leaf wax δD data from grass and herbs to the existing global δD_n-alkane database. Inclusion of these new data with the existing global dataset (n = 408) confirms plant ecological life form as an important control for leaf wax δD variation for terrestrial plants living at high latitudes. Our results suggest that, while precipitation δD is captured in these high latitude plants, physiological characters such as leaf area, venation pattern and hydraulic system, that enhance transpiration rate during summer growth, may impart δD_n-alkane differences among plants with different ecological life forms.