Compositions of n-Alkanes and Their Isotopes in Plants from the Different Latitude Regions in China

n-Alkanes and their carbon and hydrogen stable isotopes were analyzed in grasses,reeds and tree leaves from five regions with latitudes of 22° to 39° in China using GC-MS and GC-TC-IRMS techniques.The distribution of n-alkanes in the samples ranges from C15 to C35 with a high odd over even predominance and carbon-number maxima at C27,C29 or C31.The CPI values are from 3.49 to 17.25,and the mean values show a characteristic of tree leafmreedmgrass.The ACL values are between 26.24 and 30.26 and the mean values exhibit a trend of grassmreedmtree leaf.It is observed that Cmax,CPI and ACL values of n-alkanes in the studied plants from low latitude area are higher than those from high latitude area.In this study,it is found that a change of ACL units for crossing 1 latitude and increasing 1 C is 0.08 for grass,0.22 for reed and 0.36 for tree leaf and 0.04 for grass,0.24 for reed and 0.20 for tree leaf,respectively.The δ13C values of C27 and C29 n-alkanes in the studied plants ranges from-25.3‰ to-35.5‰ and the grass has a lighter mean carbon isotopic composition than the reed and tree leaf.The δD values of C27 and C29 n-alkanes in the plants are between-132.1‰ and-192.6‰ and the mean hydrogen isotopic compositions of C27 and C29 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 leaf samples from high latitude and elevation area have relatively light hydrogen isotopic composition.Therefore,Cmax,CPI and ACL values of n-alkanes in grasses,reeds and tree leaves and δD values of C27 and C29 n-alkanes in grasses and tree leaves can be used to indicate palaeoenvironmental characteristics.