Comparison of n-alkane concentrations and delta D values between leaves and roots in modern plants on the Chinese Loess Plateau

摘要

Sedimentary delta Dn-alkane values have been widely used as a valuable proxy for paleoenvironmental reconstruction. A number of studies have focused on delta D(n-alkne )values that derived exclusively from leaves, while less attention has been paid to the root-derived n-alkanes and their impact on sedimentary delta Dn-alkane values. In this study, we sampled modern plant leaf and root materials from different growth contexts (slopes and seasons) on the Chinese Loess Plateau to compare leaf-derived n-alkanes with root-derived n-alkanes. Our results demonstrated that total n-alkane (C-27-C-33) concentrations varied substantially between leaf and root materials, with average values of 209 and 29.5 mu g/g observed in leaves and roots respectively. The results suggest that ca. 12% of the n-alkane concentrations in sediments may be derived from plant roots. Furthermore, leaf-derived delta Dn-alkane values for Stipa bungeana (grass), Artemisisa vestita (shrub) and Bothriochloa ischaemum (grass) averaged -184 parts per thousand, -152 parts per thousand, and -198 parts per thousand, compared with their root-derived delta Dn-alkane values of -19 parts per thousand, -179 parts per thousand, and -163 parts per thousand, respectively. These statistically significant differences in concentrations and delta D values between leaf-derived and root-derived n-alkanes suggest that the contribution of n-alkanes derived from plant roots is important for evaluating the resultant n-alkane compositions of sediments for paleoenvironmental reconstruction. Our findings indicates that the effects of root-derived n-alkanes on total sedimentary delta Dn-alkane values should be considered carefully in future paleoenvironmental reconstruction efforts. (C) 2019 Elsevier Ltd. All rights reserved.