Wood Inter- and Intra-annual Chemical Variation

Dear Colleagues,

Wood formation is a continuous process of cell proliferation, specialization, expansion, and death, regulated by both external (photoperiod and temperature) and internal (phytohormones) factors, as well as their interactions. Annual growth rings, especially evident in the temperate zone of softwood trees, are a good example of seasonal rhythm formation associated with changes in the environment. Besides this earlywood/latewood change, the formation of juvenile and mature wood is mainly associated with internal changes, namely the maturity of the cambium. Except for a steep decrease in the extractive content and the lower lignin content in mature wood, very little is known about the variation in wood chemistry between and within growth rings. One of the main drawbacks is the large sample amount required by wet chemical methods. The development of analytical pyrolysis capable of discriminating minute chemical differences and requiring samples in the microgram range is a fine example. Spectroscopic methods can also play an important role in reducing the actual knowledge gap regarding the variation in the chemical composition at this fine level.

This will be used for the development of dendrochemistry at the biochemical level, as well as our understanding of the environment in wood chemistry.

We invite authors to contribute to this Special Issue with results on inter or intra-annual variation, as well as methodologies that could be potentially useful for this end.

Dr. José Carlos Carvalho Rodrigues
Dr. Ana Alves
Guest Editors

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• annual growth rings
• earlywood/latewood
• juvenile/mature wood
• wood chemistry
• analytical pyrolysis
• vibrational spectroscopy
• extractives
• lignin content and composition
• cellulose
• hemicelluloses

Title: Lignin content and the S/G ratio of Eucalyptus globulus vary more between trees within countries than between countries, regardless of age differences.
Authors: Ana Alves; José Rodrigues
Affiliation: Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa
Abstract: This study investigated the natural variation in lignin content and S/G ratio of Eucalyptus globulus from native Australian (AU) trees and introduced trees from Argentina (AR), Portugal (PT), and Uruguay (UY). Even though Klason lignin content (18–24%) and S/G ratio (1.58–2.41) varied considerably between trees, the differences between countries were smaller but significant: AU (20.5%; 1.97), PT (20.2%; 2.02), AR (21.7%; 1.94), and UY (21.7%; 2.16). Based on normalized data, Principal Component Analysis (PCA) of lignin pyrolysis products shows that AU and AR are in the same group and are different from PT along PC 1 (24%), which is different from UY along PC 2 (20%). The main variation along PC 1 (48%) based on mean-centred data is due to the tree-to-tree variation of the most important lignin peak, S4 (syringol, 4-propenyl-trans), which accounts for 14% of the total lignin peaks. Higher percentages of S10 (sinapinaldehyde), S1 (syringol), and S5 (syringaldehyde), which together made up 24% of lignin peaks, are primarily responsible for the differentiation of PT from AU/AR along PC 2 (21%). Age does not affect the S/G ratio, and it is unlikely to be responsible for the lignin structural differences between countries.