Successful Colonization of Lodgepole Pine Trees by Mountain Pine Beetle Increased Monoterpene Production and Exhausted Carbohydrate Reserves
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Lodgepole pine (Pinus contorta) forests have experienced severe mortality from mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) in western North America for the last several years. Although the mechanisms by which beetles kill host trees are unclear, they are likely linked to pine defense monoterpenes that are synthesized from carbohydrate reserves. However, how carbohydrates and monoterpenes interact in response to MPB colonization is unknown. Understanding this relationship could help to elucidate how pines succumb to bark beetle attack. We compared concentrations of individual and total monoterpenes and carbohydrates in the phloem of healthy pine trees with those naturally colonized by MPB. Trees attacked by MPB had nearly 300% more monoterpenes and 40% less carbohydrates. Total monoterpene concentrations were most strongly associated with the concentration of sugars in the phloem. These results suggest that bark beetle colonization likely depletes carbohydrate reserves by increasing the production of carbon-rich monoterpenes, and other carbon-based secondary compounds. Bark beetle attacks also reduce water transport causing the disruption of carbon transport between tree foliage and roots, which restricts carbon assimilation. Reduction in carbohydrate reserves likely contributes to tree mortality.
KeywordsCarbon balance Conifers Insect outbreaks Resource allocation Terpenes Tree chemical defenses Tree death
The project received funding from the NSERC-Discovery to NE, The University of Alberta – Undergraduate Research Initiative for MR. Carbohydrate analysis was conducted by Maksat Igdyrov in Dr. Simon Landhäusser’s lab (Univ. Alberta). We also acknowledge that all research presented in the manuscript was conducted in accordance with all applicable laws and rules set forth by provincial (Alberta) and federal governments and the University of Alberta and all necessary permits were in hand when the research was conducted.
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