Variation of total phenolic content and individual low-molecular-weight phenolics in foliage of mountain birch trees (Betula pubescens ssp.tortuosa)

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Abstract
We studied seasonal and between-tree variation in the composition and content of total and individual low-molecular-weight phenolics (LMWP) in leaves of mountain birch trees (Betula pubescens ssp.tortuosa). The major phenolic compounds were chlorogenic acid, quercetin-3-O-β-D-glucuronopyranoside, myricetin-3-O-(5-acetyl)-L-rhamnopyranoside, and 1-O-galloyl-β-D-(2-O-acetyl)-glucopyranose. The content of total phenolics, as well as the sum of individual LMWP, varied only slightly among trees while variation in contents of individual LMWP was large. Concentrations of almost all phenolics decreased during the growing season but pairwise correlations between individual phenolics remained similar over the whole season indicating tree-specific LMWP profiles over the season. Among flavonoids, the between-tree component of variation was 2.6 times as large as the seasonal component, while for variation of nonflavonoids the between-tree component was larger than the seasonal one. To explain the significant correlations within both flavonoid and nonflavonoid compounds, we discuss the biogenesis of LMWP in birch leaves, as well as their ecological role.