Distribution and isotopic composition of n-alkanes from grass, reed and tree leaves along a latitudinal gradient in China

Abstract

Molecular composition and compound-specific carbon and hydrogen stable isotope ratios of n-alkanes are presented for leaves of grass, reeds and trees from five regions extending between latitudes 22° and 39°, China. The distribution of n-alkanes ranges from C15 to C35 with a high odd over even predominance and carbon-number maxima at C27, C29 or C31. The carbon preference index (CPI) values are from 3.49 to 17.25, with mean values increasing following tree leaf > reed > grass. The average chain length (ACL) values are between 26.24 and 30.26 and the mean values increase following grass > reed > tree leaf. It is observed that Cmax, CPI and ACL values of n-alkanes in plants from low latitudes are higher than those from high latitudes. The δd 13C values of C27 and C29 n-alkanes in plants range from -25.3 to -35.5‰ and the grass has a lighter mean carbon isotopic composition than the reed and tree leaf. The dD values of C 27 and C29 n-alkanes in the plants are between -132.1 and -192.6‰ and the mean hydrogen isotopic compositions of C27 and C29k n-alkanes in the grass are lighter than those in the reed and tree leaves. C27 and C29 n-alkanes in the grass and tree leaves from highlatitude and elevation area have relatively lighter hydrogen isotopic composition, indicating that these δD values can be used as excellent indicators of environment and climate. Copyright © 2011 by The Geochemical Society of Japan.