A new mechanism for tree mortality due to drought and heatwaves

Hervé Cochard

doi:10.1101/531632

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.

Competing Interest Statement

The authors have declared no competing interest.

Footnotes

Cite as: Cochard, H. (2020) A new mechanism for tree mortality due to drought and heatwaves. bioRxiv, 531632, ver. 2 peer-reviewed and recommended by PCI Forest and Wood Sciences. doi: https://doi.org/10.1101/531632
Version 2 of this preprint has been peer-reviewed and recommended by Peer Community In Forest and Wood Sciences (https://doi.org/10.24072/pci.forestwoodsci.100002)

Abbreviations:

e_leaf (kPa): Vapor pressure of water in the leaf at T_leaf and ⍰_leaf
e_{sat_leaf} (kPa): Saturation vapor pressure in the leaf at T_air
e_air (kPa): Vapor pressure of water in the air at T_air
e_{sat_air} (kPa): Saturation vapor pressure of the air at T_air
E (mmol s⁻¹ m⁻²): Leaf transpiration rate
F_T (poise⁻¹): Dynamic fluidity of water
g_leaf (mmol s⁻¹ m⁻²): Maximum leaf conductance to vapor
g_min (mmol s⁻¹ m⁻²): Minimum (residual) leaf conductance
g_s (mmol s⁻¹ m⁻²): Leaf stomatal conductance
K_plant (mmol s⁻¹ MPa⁻¹): Whole plant hydraulic conductance
K_T (mmol s⁻¹ MPa⁻¹): Hydraulic conductance
P_air (kPa): Atmospheric pressure
P_leaf (MPa): Leaf turgor pressure
P₅₀ (MPa): Xylem pressure inducing 50% loss of hydraulic conductance
Q_10a: Leaf cuticle Q10 value below Tp
Q_10b: Leaf cuticle Q10 value above Tp
RH_air (%): Air relative humidity
RH_air-min (%): Minimum daily air relative humidity
RH_air-max (%): Maximum daily air relative humidity
t_g0 (s): Time to stomatal closure
t_HF (s): Time to hydraulic failure
T_air (°C): Air temperature
T_air-min (°C): Minimum daily air temperature
T_air-max (°C): Maximum daily air temperature
T_leaf (°C): Leaf temperature
Tp (°C): Leaf cuticle phase transition temperature
VPD (kPa): Vapor pressure deficit between the leaf and the air
ε (MPa): Leaf modulus of elasticity
σ_T (Nm₋₁): Water surface tension.
Ψ_leaf (MPa): Leaf water potential
Π_T (MPa): Leaf osmotic potential

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