Quantitative and qualitative composition of bark polyphenols changes longitudinally with bark maturity in Abies alba Mill.

Abstract

Key message: Total bark extractive content increases at positions higher in the trunk ofAbies albaMill. trees. The greatest proportions of bark polyphenolic extractives are found in the lower section of the trunk, below the crown. Context: The bark of commercially grown softwood trees is a potentially valuable source of secondary metabolites including polyphenols such as tannins, used in the manufacture of adhesives and resins. There is little information about how the yield and composition of bark extracts vary longitudinally within trees and with respect to the presence or absence of branches. Aims: We examined the variability of bark secondary metabolites in the softwood Abies alba both longitudinally within trees and among trees at specific sample heights. The aim was to determine whether specific bark fractions within this species contain more extractable secondary metabolites than others. Methods: Eight trees of A. alba were harvested, and up to 13 discs were cut along the trunk from 30 cm above the ground to where the trunk was only 10 cm in diameter. Milled bark was extracted with water:ethanol (1:1) using an accelerated solvent extractor and the dry yield calculated. Extract composition was examined by liquid chromatography followed by mass spectrometry. Results: Total extract yield increased from the base of the tree towards the top. The yield of the most abundant polyphenolic compounds decreased from the base of the tree towards the top, indicating the total extracts included compounds that were not detectable with the chromatographic method used. Conclusion: Although extract yield is highest at the top of the tree, the composition of the extracts indicates that compounds with known marketable value, and present in detectable proportions, are found at the base of the tree.