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Table 2 Summary of measured and derived parameters for characterizing anisohydric and isohydric responses to drought as a proxy for drought sensitivity

From: Are Northeastern U.S. forests vulnerable to extreme drought?

Citations

Measured parameters

Derived parameters

Characteristics of isohydric/anisohydric behavior

Related characteristics

Northeastern species

Loewenstein and Pallardy (1998)

Stomatal conductance (g s ), midday leaf water potential (Ψ md), predawn leaf water potential (Ψ pd)

 

Isohydric, little to no decline in Ψ md with decreasing Ψ pd due to greater stomatal closure

Anisohydric, greater decline in Ψ md with decreasing Ψ pd

Greater concentrations of abscisic acid (ABA, root origin) during drought in isohydric species

Acer saccharum (A)

Quercus alba (A)

Juglans nigra (I)

Tardieu and Simonneau (1998)

g s , leaf water potential (Ψ L )

 

Isohydric; under high evaporative demand, Ψ L reaches a plateau due to stomatal closure regardless of soil moisture conditions

Anisohydric, Ψ L declines with increasing evaporative demand and declining soil moisture with midday stomatal closure under severe water deficit

Isohydric species: g s more sensitive to ABA under high evaporative demand or water deficit. Anisohydric species: g s shows similar response to ABA regardless of evaporative demand or soil water deficit

N/A

Sperry et al. (2002)

Midday leaf water potential (Ψ md), transpiration per leaf area area (E)

 

Isohydric, constant Ψ md during high evaporative demand that is maintained above critical water potential regardless of soil moisture

Anisohydric, Ψ md declines with declining soil moisture until Ψ md approaches a critical Ψ md value

Isohydric and anisohydric species maintain smaller and larger hydraulic safety margins, respectively

N/A

Martinez-Vilalta et al. (2014)

Predawn leaf water potential (Ψ pd), Ψ md

Slope of Ψ pd − Ψ md relationship (∂Ψpd/∂Ψmd)

Isohydric, ∂Ψpd/∂Ψmd = zero

Anisohydric, ∂Ψpd/∂Ψmd > 1

∂Ψpd/∂Ψmd negatively correlated with mean summer VPD and P 50

Quercus alba (partial isohydric)

Klein (2014)

g s , Ψ L

Ψ at 50% g s of maximum g s \( \left({\varPsi}_{g_{s50}}\right) \)

Isohydric, greater \( {\varPsi}_{g_{s50}} \) across continuum

Anisohydric, lower \( {\varPsi}_{g_{s50}} \) across continuum

Isohydric species have smaller P 50

Liriodendron tulipifera (I)

Acer saccharum (intermediate)

Skelton et al. (2015)

g s , shoot water potential (Ψ), stem-specific conductivity (K s )

Ψ at 12% g s of maximum g s (P g12), Ψ at 50% loss of conductivity (P 50)

Isohydric, (P g12 − P 50) = positive

Anisohydric, (P g12 − P 50) = negative

Isohydric species maintain greater hydraulic safety margin

N/A

Roman et al. (2015)

Ψ L , soil water potential (Ψ s ), g s , VPD

∂Ψ L /∂Ψ s , ΔΨ = Ψ L  − Ψ s

Isohydric, ∂Ψ L /∂Ψ s  = 0

Anisohydric, ∂Ψ L /∂Ψ s  > 1

Isohydric species become less sensitive to VPD due to decreasing ΔΨ and g s during drought

Quercus alba (A)

Quercus rubra (A)

Acer saccharum (I)

Sassafras albidum (I)

Liriodendron tulipifera (I)

Garcia-Forner et al. (2016)

Ψ pd, Ψ md

ΔΨ = Ψ pd − Ψ md

Isohydric, less variation in ΔΨ

Anisohydric, greater variation in ΔΨ

Anisohydric species showed greater stomatal control than expected

N/A

Meinzer et al. (2016)

Ψ pd, Ψ md, leaf osmotic potential at full turgor (Ψ π 100), Leaf water potential at turgor loss point (Ψ TLP)

Hydroscape area: Area of triangle bounded by Ψ pd − Ψ md regression line and 1:1 line

Isohydric, smaller hydroscape area

Anisohydric, large hydroscape area

Hydroscape area strongly correlated with Ψ π 100 and Ψ TLP across species

N/A

  1. Additional characteristics associated with aniso- and isohydric responses are provided. Species common to the Northeastern U.S. are also provided, as well as the type of behavior
  2. A anisohydric, I isohydric, unless noted otherwise