Abstract
To decarbonize the building sector, the use of durable wood materials must be increased. Inspiration for environmentally benign wood protection systems is sought in durable tree species depositing phenolic extractives in their heartwood. Based on the hypothesis that the micro-distribution of extractives influences durability, we compared the natural impregnation patterns of non-durable, but readily available Norway spruce to more durable Kurile larch by mapping the distribution of heartwood extractives with Confocal Raman Imaging and multivariate data decomposition. Phenolics of both species were associated with hydrophobic oleoresin, likely facilitating diffusion through the tissue. They accumulated preferentially in lignin-rich sub-compartments of the cell wall. Yet, the distribution of extractives was found not to be the same. The middle lamellae contained flavonoids in larch and aromatic waxes in spruce, which was also found in rays and epithelial cells. Spruce-lignans were tentatively identified in all cell types, while larch-flavonoids were not present in resin channels, hinting at a different origin of synthesis. Larch-oleoresin without flavonoids was only found in lumina, indicating that the presence of phenolics in the mixture influences the final destination. Together our findings suggest, that spruce heartwood-defense focuses on water regulation, while the more efficient larch strategy is based on antioxidants.
Highlights
To decarbonize the building sector, the use of durable wood materials must be increased
We found that lignin surrounds epithelial cells, on the side facing the intercellular space making up the channel void
We showed a close association between oleoresin and the heartwood phenolics of both species, analogous to the observations in Scots p
Summary
To decarbonize the building sector, the use of durable wood materials must be increased. Based on the hypothesis that the micro-distribution of extractives influences durability, we compared the natural impregnation patterns of non-durable, but readily available Norway spruce to more durable Kurile larch by mapping the distribution of heartwood extractives with Confocal Raman Imaging and multivariate data decomposition Phenolics of both species were associated with hydrophobic oleoresin, likely facilitating diffusion through the tissue. The explanation lies in the identity, amount and distribution of so-called extractives deposited within the heartwood of the living trees They protect the main wood biopolymers against fungal decay, and appear to be among the compounds first targeted during initial fungal decay, as published recently in this j ournal[4]. Its composition may change in response to a fungal attack, as the constituents display antioxidative p
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