Storm-induced tree resistance and chemical differences in Norway spruce (Picea abies)

Windstorm is one of the most destructive environmental disturbance factors on forests, but its influence on conifer defense chemistry and susceptibility to insects and diseases is not well understood. We selected groups of 10 Norway spruce trees with short leaders, leaning stems, or no apparent damage 17 months after the largest storm ever recorded in Sweden. Trees were mass-inoculated with Ceratocystis polonica, a virulent blue stain fungus associated with the spruce bark beetle (Ips typographus) to estimate tree resistance. Terpene and phenolic composition in the bark was analyzed by gas chromatography-mass spectrometry, two-dimensional gas chromatography, and liquid chromatography. In contrast to our hypothesis, the results showed that trees with no apparent damage were more susceptible to C. polonica inoculation than short-leader and leaning-stem trees. Chemical composition also differed between trees in different damage classes. (+)-3-carene and two unidentified stilbenes were higher, and taxifolin glycoside was lower in trees without apparent damage than in the others. The relative amount of (-)-alpha-pinene was negatively correlated, whereas (+)-3-carene, sabinene, (-)-germacrene D, thunbergol and two unidentified stilbenes were positively correlated with fungal performance. These results suggested that wind damage had increased resistance level of short-leader and leaning trees to C. polonica inoculation, and that change in terpene and phenolic composition in the bark could be at least partly responsible for the induced resistance. Different possible explanations for this unexpected finding are discussed.