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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