Hydrophobic and hydrophilic extractives in Norway spruce and Kurile larch and their role in brown-rot degradation

Extractives found in the heartwood of a moderately durable conifer (Larix gmelinii var.
japonica) were compared with those found in a non-durable one (Picea abies). We
identified and quantified heartwood extractives by extraction with solvents of different
polarities and gas chromatography with mass spectral detection (GC-MS). Among the
extracted compounds, there was a much higher amount of hydrophilic phenolics in
larch (flavonoids) than in spruce (lignans). Both species had similar resin acid and fatty
acid contents. The hydrophobic resin components are considered fungitoxic and the
more hydrophilic components are known for their antioxidant activity. To ascertain the
importance of the different classes of extractives, samples were partially extracted prior to
subjection to the brown-rot fungus Rhodonia placenta for 2–8 weeks. Results indicated
that the most important (but rather inefficient) defense in spruce came from the fungitoxic
resin, while large amounts of flavonoids played a key role in larch defense. Possible
moisture exclusion effects of larch extractives were quantified via the equilibriummoisture
content of partially extracted samples, but were found to be too small to play any
significant role in the defense against incipient brow-rot attack.