Watertransport in plants at multiple scales: A physiological, ecological, andevolutionary appraisal
McCulloh, Kate , Johnson, Daniel , Woodruff, David , Meinzer, Frederick .
Contrasting axial patterns in xylem hydraulic traits may reflect differences in strategies for coping with daily cycles of water stress.
Our understanding of axial patterns in plant xylem structure and function varies. For example, the anatomical trend of vessel or tracheid diameters to decrease from the bottom to the tops of plants is well established in a wide variety of species across a range of growth forms. In contrast, the pattern of how vulnerability to and actual risk of embolism changes along this trajectory is not as clear and may also differ considerably more between species than the anatomical trend. In particular, when only the distal most branches and leaves are compared, some species become more vulnerable to embolism from the branches to the leaves, while other species exhibit the opposite pattern. We have examined the axial patterns of a range of functional traits, including vulnerability to embolism, hydraulic capacitance and operating ranges of xylem tension in a variety of species and supplemented this work with data from the literature. Our results suggest that the variation in the pattern of vulnerability to and occurrence of embolism among some species may reflect differences in the location of hydraulic "fuses" that embolize at pressures we would consider relatively mild and may do so on a daily basis. These fuses act to hydraulically isolate the stomata, which then are prompted to close. The hydraulic function at these fuse locations appears to be restored overnight, which likely requires energy and osmotic solutes. Not all species seem to exhibit these fuses, but there is some evidence that the location and/or existence of the fuse may be consistent within a wood type. Thus, there seems to be a tradeoff between functional groups that lose hydraulic function at fuse locations and must restore it on a daily basis, and those that construct xylem that is embolism resistant enough to avoid loss of function. By examining patterns of hydraulic vulnerability and daily dynamics of embolism across multiple organs, we can get a more complete picture of how plants cope with both daily cycles of water stress and more severe droughts.
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1 - Oregon State University, Forest Ecosystems and Society, Corvallis, OR, 97331, USA
2 - Duke University, Nicholas School of the Environment, Durham, NC, 27708, USA
3 - USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR, 97331, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware C/Hyatt
Date: Monday, July 9th, 2012
Time: 2:30 PM