Hydrogen isotopic compositions and their environmental significance for individual n-alkanes in typical plants from land in China

Abstract

Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hydrogen isotopic compositions and environmental significance. The results show that a difference in ° D values (from −42.1‰ to −66.6‰) of n-alkanes exists among the same kinds of plants from various regions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean ° D values of n-alkanes in the studied plants range from −202.6‰ to −130.7‰ and the reed from a salt marsh has the largest value. The mean ° D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean ° D values exhibit a distribution of tree leaf > reed > grass. It is observed that the mean ° D values of n-alkanes and ° D values of C27 and C29n-alkanes in the grasses and tree leaves from these studied regions correlate clearly negatively with latitude and positively with temperature, indicating that these values can be used as excellent indicators of environment and climate. These results provide important basic data for understanding the distributional law of hydrogen isotopes of individual n-alkanes and their applied research.