Browse by
Summary Table
Presenting Author
All Authors
Author's Institutions
Abstract Title
Abstract Keywords
Programs At-A-Glance
Detailed Programs
Custom Schedule
Botany 2005 Home

Abstract Detail

Biology of Dryland Plants

Hacke, Uwe G. [1], Sperry, John S. [1].

Xylem ecophysiology in the drylands.

The xylem of most dryland plants is resistant to cavitation, but often has a low conducting efficiency. This and the fact that xylem is usually not more resistant than required in a specific habitat suggests that there are costs involved in developing cavitation-resistant xylem. More negative xylem pressure requires greater wall reinforcement to prevent conduit collapse. This is reflected on the tissue level, as xeric plants typically show greater wood densities than riparian and mesic plants. Besides this mechanical cost of developing safe xylem, there is a hydraulic cost. In angiosperms, we found that resistant vessels have less pit membrane area than vulnerable ones. This suggests that cavitation is caused by the rare largest membrane pore, whose average size increases with total pit area per vessel. Total pit area was related to vessel surface area. Consequently, resistant vessels had not only less pit area than vulnerable ones, but resistant conduits were also smaller. This resulted in a trade-off between vessel resistivity and cavitation resistance. The constraint on pit area and vessel surface area also explains why vessels were not longer, and why pits accounted for c. 55% of the total xylem resistivity. In conifers, we observed a trend for decreasing tracheid diameter with increasing cavitation resistance. Although there is no known causal link between these two parameters, there may be an indirect constraint on tracheid diameter. Wider conduits require thicker walls to prevent implosion at a given xylem pressure. There may be a developmental limit to wall thickness in earlywood tracheids, which would constrain tracheid diameters in xeric species. Notably, torus-margo pits of conifers showed much greater conductances than the simpler pits of angiosperms, thus compensating to a large degree for the smaller conduit size in conifer xylem.

Log in to add this item to your schedule

1 - University of Utah, Department of Biology, 257 S. 1400 E., Salt Lake City, Utah, 84112, USA

water transport
drought resistance
xylem cavitation
transport efficiency

Presentation Type: Symposium or Colloquium Presentation
Session: 41-10
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 11:30 AM
Abstract ID:191

Copyright 2000-2005, Botanical Society of America. All rights