Study on the n-alkane patterns in some grasses and factors affecting the n-alkane patterns

Abstract

The proportions of alkanes in plant cuticular waxes are influenced by sampling date, site and grazing pressure. Alkanes in organs of major wild forage grasses in Japan were evaluated to estimate the intake and diet composition of grazing animals. Samples of four grasses from a fixed site in native grassland and three grass species from different sites were collected from June to November, to test the temporal and spatial effects on alkane concentrations. Most alkane concentrations in Miscanthus sinensis Anderss, Pleioblastus chino (Franch. Et Savat.) Makino, Sasa nipponica and Zoysia japonica increased from June to July, and then decreased to mid November. Alkane concentrations in the Z. japonica sward used to test the effects of grazing pressure decreased from May to September. Although the sampling dates affected the alkane concentrations, the species effects accounted for 70-93% of the observed variation. Grazing pressure affected only the C 29 (n-Nonacosane) alkane concentrations in dead aboveground materials of Z. japonica, but altered the ratios of C 29 :C 31 (n-Hentriacontane) in both dead and live Z. japonica. There were positive correlations between C 27 (n-Heptacosane), C 29 and C 25 (n-Pentatriacontane) alkane concentrations in live leaves of M. sinensis and of C 31 in live leaves of P. chino with growing season temperature and radiation. The concentrations of C 25 , C 27 and C 29 in dead leaves of M. sinensis and of C 33 (n-Tritriacontane) and C 25 in live Z. japonica were significantly correlated only with radiation. Alkane concentrations differed between the sampling sites, and considerable differences were observed between samples from Iwate and Kumamoto. Both live leaf and dead leaf samples from M. sinensis contained substantial amounts of C 27 , C 29 , C 31 , C 33 and C 32 , and showed that alkane concentrations in stems were much lower during the whole growing season. Although concentrations of C 29 were highest in Sasa nipponica (Makino) makino et Shibata, concentrations of C 31 or C 33 were highest in the other three grass species. Grazing pressures had little effect on alkane patterns, in which alkanes with odd-numbered carbon chains were predominant and most alkanes were of chain length C 25 (n-Pentacosane) to C 25 (n-Pentatriacontane).