Dynamics of leaf hydraulic conductance with water status: quantification and analysis of species differences under steady state

摘要

Leaf hydraulic conductance (K_leaf) is a major determinant of photosynthetic rate in well-watered and drought-stressed plants. Previous work assessed the decline of K_leaf with decreasing leaf water potential (Ψ_leaf), most typically using rehydration kinetics methods, and found that species varied in the shape of their vulnerability curve, and that hydraulic vulnerability correlated with other leaf functional traits and with drought sensitivity. These findings were tested and extended, using a new steady-state evaporative flux method under high irradiance, and the function for the vulnerability curve of each species was determined individually using maximum likelihood for 10 species varying strongly in drought tolerance. Additionally, the ability of excised leaves to recover in K_leaf with rehydration was assessed, and a new theoretical framework was developed to estimate how rehydration of measured leaves may affect estimation of hydraulic parameters. As hypothesized, species differed in their vulnerability function. Drought-tolerant species showed shallow linear declines and more negative Ψ_leaf at 80% loss of K_leaf (P₈₀), whereas drought-sensitive species showed steeper, non-linear declines, and less negative P₈₀. Across species, the maximum K_leaf was independent of hydraulic vulnerability. Recovery of K_leaf after 1 h rehydration of leaves dehydrated below their turgor loss point occurred only for four of 10 species. Across species without recovery, a more negative P₈₀ correlated with the ability to maintain K_leaf through both dehydration and rehydration. These findings indicate that resistance to K_leaf decline is important not only in maintaining open stomata during the onset of drought, but also in enabling sustained function during drought recovery.