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Combined drought and bark beetle attacks deplete non-structural carbohydrates and promote death of mature pine trees
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  • Nadir Erbilgin,
  • Leila Zanganeh,
  • Jennifer Klutsch,
  • Shih-hsuan Chen,
  • Shiyang ZHAO,
  • Guncha Ishangulyyeva,
  • Stephen Burr,
  • Monica Gaylord,
  • Richard Hofstetter,
  • Ken Keefover-Ring,
  • Kenneth F. Raffa,
  • Thomas Kolb
Nadir Erbilgin
University of Alberta
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Leila Zanganeh
University of Alberta
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Jennifer Klutsch
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Shih-hsuan Chen
University of Alberta
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Shiyang ZHAO
University of Alberta
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Guncha Ishangulyyeva
University of Alberta
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Stephen Burr
USDA Forest Service Alaska Region
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Monica Gaylord
USDA Forest Service Flagstaff Forestry Sciences Laboratory
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Richard Hofstetter
Northern Arizona University
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Ken Keefover-Ring
University of Wisconsin Madison
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Kenneth F. Raffa
University of Wisconsin Madison
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Thomas Kolb
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Abstract

How carbohydrate reserves change in conifers during drought and bark beetle attacks are poorly understood. We investigated changes in carbohydrate reserves and carbon-dependent terpene defenses in ponderosa pine trees experimentally subjected to two levels of drought stress (via root trenching) and two types of biotic challenge treatments (pheromone-induced bark beetle attacks or inoculations with crushed beetles that include beetle-associated fungi) for two consecutive years. Our results showed that trenching did not influence carbohydrates whereas both biotic challenges reduced amounts of starch and sugars of trees. However, only the trenched-beetle attacked trees depleted carbohydrates and died within the first year of bark beetle attacks. While live trees contained higher carbohydrates than dying trees, amounts of constitutive and induced terpenes produced did not vary between live and beetle-attacked dying trees, respectively. Based on these results we propose that reallocation of carbohydrates to terpenes during the early stages of beetle attacks is limited in drought-stricken trees, and that the combination of biotic and abiotic stress leads to tree death. The process tree death is subsequently aggravated by beetle girdling of phloem, occlusion of vascular tissue by bark beetle-vectored fungi, and potential exploitation of host carbohydrates by beetle symbionts as nutrients.