Field variations in alkane signatures among plant species in ‘degraded’ and perennial pastures on the Northern Tablelands of New South Wales

Abstract

Differences in concentrations of n-alkanes in the cuticular waxes of plants can be used to estimate the species composition of herbage mixtures or the diet consumed by grazing animals. The objectives of this study were (i) to provide information on the n-alkane (C25-C35) ‘signatures’ or patterns of pasture species occurring in ‘degraded’ and perennial pastures of the Northern Tablelands, New South Wales, and (ii) to examine the extent of the field variation in the signatures. There were considerable differences in odd-numbered alkanes and in their total content between species. There were also significant differences in n-alkane concentrations among species within grasses, legumes, and weeds. For the individual odd-numbered alkanes, differences between species accounted for 87-93% of the total variance in alkane concentration over 3 samplings. Variable results for the temporal effect suggest that time-specific herbage samples are needed in animal diet studies. Analyses of the spatial effect indicate that random cuts over each treatment plot can obtain representative samples of each species. Multivariate statistical analyses using principal component and discriminant analyses indicated that the patterns of alkanes in species occurring on both degraded and perennial pastures were readily distinguishable. These results confirmed that the alkane technique could be used for estimation of diet composition in grazing sheep on the Northern Tablelands, NSW, where differences in n-alkane signatures between species were sufficient and persistent over time.