Using the n-alkanes of plant cuticular wax to estimate the species composition of herbage mixtures

Abstract

This study examined whether or not between-species differences in the concentrations of saturated hydrocarbons (n-alkanes) in the cuticular wax of pasture species could be exploited to estimate the species composition of herbage mixtures. Six sets of mixtures were prepared, containing either two, three or four species. The levels of cuticular wax alkanes were estimated in samples of the pure species and the mixtures, and used in simultaneous equations to compute species composition. The levels of Lolium perenne and Trifolium subterraneum in mixtures of these two species were accurately estimated from alkane analyses, as were the levels of these two species and Holcus lanatus when all three were mixed. In mixtures of T. subterraneum, L. rigidum and Phalaris aquatica, the first two species were well estimated, but phalaris was under-estimated, perhaps because of its relatively low alkane levels. In mixtures of these three species and Medicago sativa, the amounts of the grass species were estimated accurately, but the two legume species were not well distinguished from each other. However, total legume content was estimated very accurately. The species composition of mixtures of T. subterraneum and the above three grasses was also accurately estimated. It is concluded that the use of cuticular wax alkanes should allow a greater differentiation of herbage mixtures into their component species than was possible in previous studies using other markers. Results are also presented to indicate that ratios of alkane concentrations, especially the ratio of C29:C33 alkanes, can also be used to quantify, or at least rank, the clover content of herbage mixtures.