Foliar phenolic composition of European white birch during bud unfolding and leaf development.

We studied the between-tree and within-tree variation in the composition and content of foliar low-molecular-weight phenolics (LMWP) of European white birch (Betula pendula Roth) during the unfolding of vegetative buds and during early leaf development. In buds, the major groups of phenolic compounds were hydrolysable tannins and flavonoid aglycones, whereas, later during leaf development, the flavonoid glycosides accounted for most of the total LMWP. The content of total LMWP, as well as individual compounds, varied largely among individual trees, while variation within an individual tree was low. The biosynthetic origin of individual compounds or compound groups is discussed in order to explain the main patterns in leaf chemistry during bud unfolding and early leaf development.