Mechanisms of plant survival and mortality during drought: why do some plants survive while others succumb to drought?

Abstract

Contents Summary1I.Introduction2II. Consequences of vegetation mortality3III.Global patterns of mortality3IV.Hypotheses on mechanisms of drought‐related mortality4V.Evidence for hypothesized mechanisms5VI.Implications of future climate on hypothesized mortality mechanisms13VII.Conclusions15Acknowledgements15References15 Summary 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.

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

“…Carbon reserves are hypothesized to play a role in the tolerance of environmental stress, especially when carbon gain is limited (McDowell et al. 2008; Anderegg et al. 2012; O'Brien et al.…”

“…Carbon balance is vital to plant performance, and stress‐induced NSC depletion could be a mechanism underlying tree mortality (McDowell et al. 2008; Breshears et al. 2009; Sala et al.…”

“…A synthesis of mortality mechanisms suggests two related hypotheses of drought‐induced mortality: carbon starvation and hydraulic failure (McDowell et al. 2008). Drought can have direct consequences such as embolism, hydraulic failure, and cell failure (Bréda et al.…”

“…When carbon is no longer available to sustain basic functions, a tree may die of carbon starvation (McDowell et al. 2008; Breshears et al. 2009; Adams et al.…”

“…For drought tolerance, species differences in the regulation of water loss could result in differences in the risk of carbon starvation versus hydraulic failure (McDowell et al. 2008), and the two mechanisms likely interact (McDowell 2011; Sevanto et al. 2014).…”