© 1997 Heron Publishing—Victoria, Canada
Xylem cavitation and loss of hydraulic conductance in western hemlock following planting
K. L. Kavanagh (1, 2) and J. B. Zaerr (3)
1. Department of Forest Resources, Oregon State University, Corvallis, OR 97331, USA / 2. OSU Extension Service, P.O. Box 207, Astoria, OR 97193, USA / 3. Department of Forest Science, Oregon State University, Corvallis, OR 97331, USA / Received February 2, 1996
Summary
Following planting, western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings experience water stress and declining xylem pressure potential (Ψx). Low Ψx can result in xylem cavitation and embolism formation, causing a decline in hydraulic conductance. This study focused on
the relationship between Ψx, xylem cavitation and transpiration (E) of newly planted seedlings. Leaf specific hydraulic conductance (kAB) declined from 0.56 to 0.09 mmol m–2 s–1 MPa–1 over a 9-day period. Stomatal conductance (gs) declined from 143.5 to 39.15 mmol m–2 s–1 over the same period without an associated change in environmental conditions. A vulnerability profile indicated a 30% loss
in hydraulic conductivity when seedlings experienced a Ψx between –2.5 and –3.0 MPa. A Ψx of –4.0 MPa led to a complete loss of conductivity. We conclude that following planting, western hemlock seedlings often
experience Ψx values that are low enough to cause xylem cavitation and a decline in kAB.
Keywords:
transpiration, Tsuga heterophylla, water stress vulnerability.
