Pacific Northwest Research Station

Title: Evidence for xylem embolism as a primary factor in dehydration-induced declines in leaf hydraulic conductance

Author: Johnson, Daniel M.; McCulloh, Katherine A.; Woodruff, David R.; Meinzer, Frederick C.

Date: 2012

Source: Plant, Cell and Environment. 35: 760-769

Description: Hydraulic conductance of leaves (K_leaf) typically decreases with increasing water stress and recent studies have proposed different mechanisms responsible for decreasing K_leaf. We measured K_leaf concurrently with ultrasonic acoustic emissions (UAEs) in dehydrating leaves of several species to determine whether declining K_leaf was associated with xylem embolism. In addition, we performed experiments in which the surface tension of water in the leaf xylem was reduced by using a surfactant solution. Finally, we compared the hydraulic vulnerability of entire leaves with the leaf lamina in three species. Leaf hydraulic vulnerability based on rehydration kinetics and UAE was very similar, except in Quercus garryana. However, water potentials corresponding to the initial decline in K_leaf and the onset of UAE in Q. garryana were similar. In all species tested, reducing the surface tension of water caused K_leaf to decline at less negative water potentials compared with leaves supplied with water. Microscopy revealed that as the fraction of embolized xylem increased, K_leaf declined sharply in Q. garryana. Measurements on leaf discs revealed that reductions in lamina hydraulic conductance with dehydration were not as great as those observed in intact leaves, suggesting that embolism was the primary mechanism for reductions in K_leaf during dehydration.

Keywords: cavitation, drought stress, transpiration, water potential

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Citation

Johnson, Daniel M.; McCulloh, Katherine A.; Woodruff, David R.; Meinzer, Frederick C.  2012.  Evidence for xylem embolism as a primary factor in dehydration-induced declines in leaf hydraulic conductance.   Plant, Cell and Environment. 35: 760-769.