A new mechanism for tree mortality due to drought and heatwaves

Abstract

Plants tend to die earlier in hot and drought conditions, but the underlying mechanisms are not yet understood. I propose here a new mechanism by which excessive residual water losses caused by high cuticular permeabilities and a high leaf-to-air vapor pressure deficits would trigger uncontrolled and sudden cavitation events. The combination of heat and drought stresses may therefore lead to an unsuspected risk of hydraulic failure. I explored this hypothesis with a new mechanistic model. The simulations support this hypothesis and highlight the critical role played by the cuticle phase transition temperature. Experiments are now awaited to confirm these predictions.

Different ways to die in a changing world: Consequences of climate change for tree species performance and survival through an ecophysiological perspective

“…For most species, especially the nondesert ones, g min rates tend to show small variations at temperatures from 15 to 35°C, while temperatures above 35° induce a drastic increase in cuticle permeability and, consequently, in water loss (Schreiber, ; Schuster et al, ). This abrupt increase in g min rates under a certain temperature threshold, also known as transition temperature (Schuster et al, ), can have a catastrophic effect on plants exposed to heat waves, especially under drought conditions, since the increase in water loss can significantly increase the tension in xylem vessels, which can result in a reduction in the time to HF (Cochard, ). However, despite the great impact that the increase in atmospheric temperature can have on g min rates (Bueno et al, ; Schuster et al, ) and, thus, on plant survival (Cochard, ), key questions regarding this topic remain.…”

“…This abrupt increase in g min rates under a certain temperature threshold, also known as transition temperature (Schuster et al, ), can have a catastrophic effect on plants exposed to heat waves, especially under drought conditions, since the increase in water loss can significantly increase the tension in xylem vessels, which can result in a reduction in the time to HF (Cochard, ). However, despite the great impact that the increase in atmospheric temperature can have on g min rates (Bueno et al, ; Schuster et al, ) and, thus, on plant survival (Cochard, ), key questions regarding this topic remain. For example, we currently do not have enough information to answer to which extent plants acclimated to high temperatures can alter the physicochemical properties of their cuticle in order to increase the transition temperature.…”

“…Nevertheless, even after the complete stomatal closure, the plants keep losing water to the atmosphere through their cuticle (Bueno et al, 2019). This residual transpiration (g min ) varies widely across species and functional groups (Schuster, Burghardt, & Riederer, 2017), and can directly affect the time to HF (Cochard, 2019). However, although g min has been recently pointed as a central component of the drought tolerance strategy (Cochard, 2019), several questions regarding this trait remain.…”

“…This residual transpiration (g min ) varies widely across species and functional groups (Schuster, Burghardt, & Riederer, 2017), and can directly affect the time to HF (Cochard, 2019). However, although g min has been recently pointed as a central component of the drought tolerance strategy (Cochard, 2019), several questions regarding this trait remain. For example, what are the main determinants of the variability of g min across species?…”

Hydraulics in the 21st century

“…Third, we need to better understand hydraulic fluxes and degree of associated embolism during periods when root water uptake and transpiration are curtailed and cuticular conductance and capacitance dominate the output and input fluxes of water to the foliage (Blackman et al ., ; Duursma et al ., ; Körner, ). It is these small fluxes that may define the critical point of hydraulic failure during drought (Cochard, ), and thus more detailed focus is merited. Finally, determining the role of carbohydrate supply and utilization in embolism avoidance and repair/regrowth of xylem (Vandegehuchte et al ., ; Tomasella et al ., ) is essential if we are to understand and simulate coupled carbon‐hydraulic function (McDowell et al ., ; Fisher et al ., ).…”