Is vulnerability segmentation at the leaf-stem transition a drought resistance mechanism? A theoretical test with a trait-based model for Neotropical canopy tree species

Table 1 List of traits, abbreviations, and formula when appropriate

Abbreviation	Unit	Trait	Formula
t_crit	h	Shoot desiccation time	See materials and methods
P_88,stem	MPa	Water potential at stem 88% loss of conductivity
P_88,leaf	MPa	Water potential at leaf 88% loss of conductivity
P_50,stem	MPa	Water potential at stem 50% loss of conductivity
P_50,leaf	MPa	Water potential at leaf 50% loss of conductivity
Ψ_tlp	MPa	Water potential at leaf turgor loss point
A_leaf	m²	Shoot leaf area
A_bark	m²	Stem bark area
V_stem	m³	Stem volume
g_min	mmol m⁻² s⁻¹	Leaf minimum conductance
g_bark	mmol m⁻² s⁻¹	Bark conductance
W_ft,stem	mmol m⁻³ MPa⁻¹	Estimated stem capacitance at full turgor	W_ft,stem = − 930.93 * wood density + 868.97^a
W_tlp,leaf	mmol m⁻³ MPa⁻¹	Leaf capacitance after turgor loss point
SHSM	MPa	Stomatal-hydraulic safety margin	Ψ_tlp—P_88,stem or Ψ_tlp – P_50,stem
g_min*2A_leaf^b	mmol s⁻¹	Leaf minimum transpiration rate
g_bark*A_bark	mmol s⁻¹	Bark transpiration rate
C_shoot A_leaf+bark^−1b	mmol MPa⁻¹ m⁻²	Shoot capacity to total evaporative surface	(W_ft,stemV_stem + W_tlp,leafA_leaf)/(2A_leaf + A_bark)^b
C_stem A_bark⁻¹	mmol MPa⁻¹ m⁻²	Stem capacity to bark surface	W_ft,stemV_stem/A_bark

^aSantiago et al. (2018)
^bA_leaf is multiplied by 2 as transpiration occurs at both abaxial and adaxial leaf sides