Monthly changes in chain length distributions and stable carbon isotope composition of leaf n-alkanes during growth of the bamboo Dendrocalamus ronganensis and the grass Setaria viridis

The links between growth condition change, molecular distributions and δ13C values of individual n-alkanes from leaves of the C3 bamboo Dendrocalamus ronganensis Q.H. Dai and D.Y. Huang and the C4 grass Setaria viridis (L.) Beauv. were studied to improve interpretation of the paleoenvironmental signatures of plant wax n-alkanes in sediments and soils. The molecular composition and isotopic composition of the dominant n-alkanes in fresh leaves sampled every month over the growing seasons of the plants were determined and compared against climate conditions. The average n-alkane chain length from both species was lower in the early stages of the growing season and became larger in the summer months with higher temperature and lower precipitation. The δ13C values of C27 and C29 from the leaves of D. ronganensis and of C29 and C33 from the leaves of S. viridis correlated with monthly mean temperature and precipitation amount. The isotope differences between the two dominant long chain n-alkanes in both plant species also showed positive correlation with mean monthly temperatures. The δ13C values for individual n-alkanes and especially the isotope difference between two individual n-alkanes may be good proxies for reconstructing paleoenvironmental conditions from plant wax components in geological archives.