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Harvard Forest Symposium Abstract 2006
- Title: Leaf hydraulic conductance is highly variable and sensitive to leaf water potential
- Primary Author: Timothy Brodribb (Harvard University)
- Additional Authors: Noel Michele Holbrook (Harvard Forest)
- Abstract:
The conductance of transpiring leaves to liquid water (K(leaf)) was measured across a range of steady-state leaf water potentials (Psi(leaf)) for the first time. Manipulating the transpiration rate in excised leaves enabled us to produce a range of Psi(leaf) from a few bars to minimum values of less than -1.5 MPa whilst using a flowmeter to monitor the transpiration stream. Employing this technique to measure how desiccation affects K(leaf) in 19 species, from a range of temperate and tropical habitats and including lycophytes, ferns, gymnosperms and angiosperms, we found two characteristic responses. Three of the six angiosperm species sampled maintained a steady maximum K(leaf) whilst Psi(leaf) remained above -1.2 MPa, although desiccation of leaves beyond this point resulted in a rapid decline in K(leaf). In all other species measured, declining Psi(leaf) led to a proportional decrease in K(leaf), such that midday Psi(leaf) of unstressed plants the field was sufficient to depress K(leaf) by an average of 37%. Maximum K(leaf), estimated from the linear function relating Kleaf to Psi(leaf), was strongly correlated with maximum CO2 assimilation rate, whilst K(leaf) = 0 occurred at a Psi(leaf) slightly less negative than at leaf turgor loss. A strong linear correlation between Psi(leaf) at turgor loss and Psi(leaf) at K(leaf) = 0 raises the possibility that declining Kleaf was related to declining cell turgor in the leaf prior to the onset of vein cavitation. Further, a comparison of K(leaf) vulnerability measured under steady-state evaporation and Psi(leaf) vulnerability measured by Psi(leaf) relaxation suggested that the tissue responsible for K(leaf) depression was located in the vicinity of the bundle sheath.
- Research Category: Physiological Ecology, Population Dynamics, and Species Interactions
