The n-alkane concentrations in buds and leaves of browsed broadleaf trees

The concentration of n-alkanes in the cuticular wax of plants can be used to estimate the composition of the diet selected by free-ranging animals. The aims of this study were to characterize the n-alkane profiles of developing leaves and evaluate the degree of chemical discrimination between six browsed broadleaf tree species: European ash (Fraxinus excelsior L.), flowering ash (Fraxinus ornus L.), hornbeam (Carpinus betulus L.), hazel (Corylus avellana L.), mountain ash (Sorbus aucuparia L.) and beech (Fagus sylvatica L). The effect of the stage of development was examined by considering five different vegetative stages: dormant bud (DB), late bud (LB), young leaf (YL), mature leaf (ML) and senescing leaf (SL). Five samples per each vegetative stage and species, gathered in a mixed woodland of the Italian Eastern Alps between February and October, were analysed for their n-alkane concentrations (C23-C36). The residual coefficient of variation was 15.5% on average for the individual n-alkanes considered. There were noticeable differences in individual and total n-alkanes content between species. In particular, C27 was the predominant n-alkane in beech and C33 was found in high proportions in the two species of Fraxinus; hazel and flowering ash had a higher total n-alkanes content than the overall mean, while the lowest values were found in hornbeam and beech. The n-alkane profile also underwent important changes during the vegetative development, with different extent and direction according to the species. In the three successive leaf stages, a tendency for a progressive increase in the longest chain homologues was observed. In any case, the young leaf stage differed most from the contiguous stages. Canonical discriminant analysis indicated that the n-alkane profile of buds and leaves were mathematically distinguishable and the chemical differences between species were persistent over the plant vegetative development.