Mechanisms of Plant Survival and Mortality during Drought: Why Do Some Plants Survive While Others Succumb to Drought?. McDowell, N., Pockman, W. T., Allen, C. D., Breshears, D. D., Cobb, N., Kolb, T., Plaut, J., Sperry, J., West, A., Williams, D. G., & Yepez, E. A. 178(4):719–739.
Mechanisms of Plant Survival and Mortality during Drought: Why Do Some Plants Survive While Others Succumb to Drought? [link]Paper  doi  abstract   bibtex   
Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, prediction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric regulation of water status results from avoidance of drought-induced hydraulic failure via stomatal closure, resulting in carbon starvation and a cascade of downstream effects such as reduced resistance to biotic agents. Mortality by hydraulic failure per se may occur for isohydric seedlings or trees near their maximum height. Although anisohydric plants are relatively drought-tolerant, they are predisposed to hydraulic failure because they operate with narrower hydraulic safety margins during drought. Elevated temperatures should exacerbate carbon starvation and hydraulic failure. Biotic agents may amplify and be amplified by drought-induced plant stress. Wet multidecadal climate oscillations may increase plant susceptibility to drought-induced mortality by stimulating shifts in hydraulic architecture, effectively predisposing plants to water stress. Climate warming and increased frequency of extreme events will probably cause increased regional mortality episodes. Isohydric and anisohydric water potential regulation may partition species between survival and mortality, and, as such, incorporating this hydraulic framework may be effective for modeling plant survival and mortality under future climate conditions. [Excerpt:Implications of future climate on hypothesized mortality mechanisms] [...] Warmer air temperature will exacerbate the impact of drought on plant water loss by elevating the vapor pressure deficit of the atmosphere (D), thereby placing a greater demand on transpiration [...] Rising surface temperatures could also facilitate carbon losses to maintenance respiration as a result of the exponential dependency of respiration on temperature [...] if temperature acclimation does not keep up with temperature changes [...], effectively reducing the time plants may survive on stored carbohydrates. Therefore, increased intensity and duration of future droughts will increase rates of mortality by either hydraulic failure or carbon starvation. [] A logical hypothesis is that the increased droughts predicted to occur over the next century will initially result in increased mortality of isohydric species because these species have shown greater susceptibility to drought. However, droughts of sufficient intensity could push anisohydric species past their threshold for hydraulic failure [...]. [] [...] [] Climate change-driven drought will also increase tree mortality via wildfires, both directly through combustion and, more pertinent to this review, indirectly via structural damage that predisposes trees to biotic attack [...] For trees that survive, fire reduces whole-tree leaf area and subsequent photosynthesis and carbon allocation to insect defenses [...] and may increase olfactory signals [...], leading to preferential attack from biotic agents such as bark beetles [...]. Mortality of fire-damaged trees with low resin defenses caused by bark beetle attacks is likely a consequence of carbon starvation in which the source of low carbon reserves is defoliation from drought-associated fire, rather than from prolonged stomatal closure. Future fires will preferentially shift the landscape towards species that can resprout or quickly recolonize. [] [...]
@article{mcdowellMechanismsPlantSurvival2008,
  title = {Mechanisms of Plant Survival and Mortality during Drought: Why Do Some Plants Survive While Others Succumb to Drought?},
  author = {McDowell, Nate and Pockman, William T. and Allen, Craig D. and Breshears, David D. and Cobb, Neil and Kolb, Thomas and Plaut, Jennifer and Sperry, John and West, Adam and Williams, David G. and Yepez, Enrico A.},
  date = {2008-06},
  journaltitle = {New Phytologist},
  volume = {178},
  pages = {719--739},
  issn = {0028-646X},
  doi = {10.1111/j.1469-8137.2008.02436.x},
  url = {http://mfkp.org/INRMM/article/2698660},
  abstract = {Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, prediction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric regulation of water status results from avoidance of drought-induced hydraulic failure via stomatal closure, resulting in carbon starvation and a cascade of downstream effects such as reduced resistance to biotic agents. Mortality by hydraulic failure per se may occur for isohydric seedlings or trees near their maximum height. Although anisohydric plants are relatively drought-tolerant, they are predisposed to hydraulic failure because they operate with narrower hydraulic safety margins during drought. Elevated temperatures should exacerbate carbon starvation and hydraulic failure. Biotic agents may amplify and be amplified by drought-induced plant stress. Wet multidecadal climate oscillations may increase plant susceptibility to drought-induced mortality by stimulating shifts in hydraulic architecture, effectively predisposing plants to water stress. Climate warming and increased frequency of extreme events will probably cause increased regional mortality episodes. Isohydric and anisohydric water potential regulation may partition species between survival and mortality, and, as such, incorporating this hydraulic framework may be effective for modeling plant survival and mortality under future climate conditions.

[Excerpt:Implications of future climate on hypothesized mortality mechanisms] [...] Warmer air temperature will exacerbate the impact of drought on plant water loss by elevating the vapor pressure deficit of the atmosphere (D), thereby placing a greater demand on transpiration [...] Rising surface temperatures could also facilitate carbon losses to maintenance respiration as a result of the exponential dependency of respiration on temperature [...] if temperature acclimation does not keep up with temperature changes [...], effectively reducing the time plants may survive on stored carbohydrates. Therefore, increased intensity and duration of future droughts will increase rates of mortality by either hydraulic failure or carbon starvation.

[] A logical hypothesis is that the increased droughts predicted to occur over the next century will initially result in increased mortality of isohydric species because these species have shown greater susceptibility to drought. However, droughts of sufficient intensity could push anisohydric species past their threshold for hydraulic failure [...].

[] [...]

[] Climate change-driven drought will also increase tree mortality via wildfires, both directly through combustion and, more pertinent to this review, indirectly via structural damage that predisposes trees to biotic attack [...] For trees that survive, fire reduces whole-tree leaf area and subsequent photosynthesis and carbon allocation to insect defenses [...] and may increase olfactory signals [...], leading to preferential attack from biotic agents such as bark beetles [...]. Mortality of fire-damaged trees with low resin defenses caused by bark beetle attacks is likely a consequence of carbon starvation in which the source of low carbon reserves is defoliation from drought-associated fire, rather than from prolonged stomatal closure. Future fires will preferentially shift the landscape towards species that can resprout or quickly recolonize. 

[] [...]},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-2698660,~to-add-doi-URL,abiotic-factors,array-of-factors,biotic-factors,climate-change,climate-extremes,complexity,die-off,droughts,extreme-events,extreme-weather,forest-fires,forest-pests,forest-resources,habitat-suitability,temperature,tree-mortality,vegetation,wildfires},
  number = {4}
}

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