Quantitative and qualitative composition of bark polyphenols changes longitudinally with bark maturity in Abies alba Mill.
Total bark extractive content increases at positions higher in the trunk of Abies alba Mill. trees. The greatest proportions of bark polyphenolic extractives are found in the lower section of the trunk, below the crown.
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.
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.
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.
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.
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.
KeywordsBark extractives Catechin LC-MS Silver fir Tannin Within-tree variability
The authors warmly thank Antoine Billard, Rodolphe Bauer, Fleur Longuetaud and Frederic Mothe who managed the tree sampling and Adrien Contini, Antoine Sarrouille and Coline Lebreton for their technical support. Thanks also to ONF (the French National Forest Service) who provided the material from the Saint-Prix forest.
The authors gratefully acknowledge the Lab of Excellence ARBRE for the post-doctoral fellowship granted to the first author. The UMR 1434 Silva and EA 4370 LERMAB are supported by a grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” programme (ANR-11-LABX-0002-01, Lab of Excellence ARBRE) in the frame of the project “BARK-TAN-BIO” included in the wider project “EXTRAFOREST” supported in addition by the French Ministry of Agriculture, the Lorraine-FEDER, ADEME and Grand Est Region.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interests.
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