© 1999 Heron Publishing—Victoria, Canada
Shoot and root vulnerability to xylem cavitation in four populations of Douglas-fir seedlings
K. L. Kavanagh (1), B. J. Bond (2), S. N. Aitken (3), B. L. Gartner (4) and S. Knowe (5)
1. OSU Forestry Extension Service, P.O. Box 207, Astoria, OR 97103, USA (kavanagk@oes.orst.edu) / 2. Department of Forest Science, Oregon State University, Corvallis, OR 97331-7501, USA / 3. Department of Forest Sciences, University of British Columbia, Vancouver, B.C. V6R 4K2, Canada / 4. Department of Forest Products, Oregon State University, Corvallis, OR 97331-7402, USA / 5. Rayonier Forest Research Center, P.O. Box 819, Yulee, FL 32041-0819, USA / Received December 9, 1997
Summary
The objectives of this study were to assess the range of genotypic variation in the vulnerability of the shoot and root xylem
of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings to water-stress-induced cavitation, and to assess the trade-off between vulnerability to cavitation
and conductivity per unit of stem cross-sectional area (ks), both within a species and within an individual tree. Douglas-fir occupies a broad range of environments and exhibits considerable
genetic variation for growth, morphology, and drought hardiness. We chose two populations from each of two varieties (the
coastal var. menziesii and the interior var. glauca) to represent environmental extremes of the species. Vulnerability curves were constructed for shoots and roots by plotting
the percentage loss in conductivity versus water potential. Vulnerability in shoot and root xylem varied genetically with
source climate. Stem xylem differed in vulnerability to cavitation between populations; the most mesic population, coastal
wet (CW), was the most susceptible of the four populations. In the roots, the most vulnerable population was again CW; the
interior wet (IW) population was moderately susceptible compared with the two dry populations, coastal dry (CD) and interior
dry (ID). Root xylem was more susceptible to cavitation than stem xylem and had significantly greater ks. The trade-off between vulnerability to cavitation and ks, however, was not evident across populations. The most vulnerable population (CW) had a shoot ks of 0.534 ± 0.067 μmol m–2 s–1 MPa–1, compared with 0.734 ± 0.067 μmol m–2 s–1 MPa–1 for the less vulnerable CD stems. In the roots, IW was more vulnerable than ID, but had the same ks.
Keywords:
conductivity, cross-sectional area, mesic versus xeric environments, stomata.
