Nonstructural carbohydrate dynamics of lodgepole pine dying from mountain pine beetle attack

Abstract

Bark beetle outbreaks are an important cause of tree death, but the process by which trees die remains poorly understood. The effect of beetle attack on whole-tree nonstructural carbohydrate (NSC) dynamics is particularly unclear, despite the potential role of carbohydrates in plant defense and survival. We monitored NSC dynamics of all organs in attacked and protected lodgepole pines (Pinus contorta) during a mountain pine beetle (Dendroctonus ponderosae) outbreak in British Columbia, starting before beetle flight in June 2011 through October 2012, when most attacked trees had died. Following attack, NSC concentrations were first reduced in the attacked region of the bole. The first NSC reduction in a distant organ appeared in the needles at the end of 2011, while branch and root NSC did not decline until much later in 2012. Attacked trees that were still alive in October 2012 had less beetle damage, which was negatively correlated with initial bark sugar concentrations in the attack region. The NSC dynamics of dying trees indicate that trees were killed by a loss of water conduction and not girdling. Further, our results identify locally reduced carbohydrate availability as an important mechanism by which stressors like drought may increase tree susceptibility to biotic attack.

Dead or Alive? Using Membrane Failure and Chlorophyll a Fluorescence to Predict Plant Mortality from Drought

“…S11C) shows how leaf water potential was not significantly correlated to death assessed as complete browning of the needles. For spruce only, undamaged green needles from the field were analyzed because this species turns yellow and loses its deleted needles upon beetle attack (Wiley et al, 2016). Interestingly, the percent of electrolyte leakage results pooled from all field samples showed two peaks in the lower and upper ends of the distribution (Supplemental Fig.…”

“…Lodgepole pine (Pinus contorta) and Engelmann spruce (Picea engelmannii) branch samples were harvested from the field during the summers of 2013 and 2014. Samples were collected from a variety of field sites located on Wyoming's Medicine Bow Mountain, 55 km west of Laramie, WY (41°2093999N, 106°1294799W) with altitude ranging from 2700 to 3200 m. Sampled trees included a variety of ages, dominances, and health statuses due to attack by bark beetles, species Dendroctonus ponderosae and Dendroctonus rufipennis, which cause mortality by hydraulic failure from blue-stain fungal occlusion of xylem (Wiley et al, 2016;Hubbard et al, 2013;Frank et al, 2014). Immediately after branch collection, needles were removed to test chlorophyll a fluorescence, water potential, carbohydrates, and electrolyte leakage.…”

A synthesis of radial growth patterns preceding tree mortality

“…The slower growth signal associated with mortality induced by bark‐beetle outbreaks may reflect a negative effect of carbon allocation to growth rather than defense on tree survival (growth–differentiation balance hypothesis; Herms & Mattson, ) and could be explained by several hypotheses. First, the disruptions of carbohydrate transport due to phloem feeding by bark‐beetles and xylem occlusion by the fungi they introduce (Hubbard et al ., ) usually have major consequences for tree functioning, leading to leaf shedding and tree death within a few years (Meddens et al ., ; Wiley et al ., ). Second, in the endemic phase, bark‐beetles may not preferentially attack trees with slow growth (Sangüesa‐Barreda et al ., ; but see Macalady & Bugmann, ), but rather trees with specific size and/or bark thickness, and with lower defense capacities (less resin duct production; Kane & Kolb, ; Ferrenberg et al ., ).…”

Tree defence and bark beetles in a drying world: carbon partitioning, functioning and modelling

“…However, the activation, synthesis and accumulation of combined constitutive and induced SMs may be too slow to reach effective levels against mass‐attacking beetles and prevent lethal damage, when populations are high (Boone et al ., ). In addition, field studies have shown that local NSC storage was used for production of induced SMs in response to simulated or actual bark beetle attack (Raffa et al ., ; Roth et al ., ) or fungal infection (Goodsman et al ., ; Arango‐Velez et al ., ), while NSC stored in distant organs could not be mobilized to attacked stem sections (Wiley et al ., ). Such results indicate that mobilization and transport of NSC play an important role in allocation to induced defence in conifers.…”