© 1995 Heron Publishing—Victoria, Canada
Xylem cavitation in Scots pine and Sitka spruce saplings during water stress
G. E. Jackson (1, 2), J. Irvine (1) and J. Grace (1)
1. Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, Mayfield Road, Edinburgh EH9 3JU,
U.K. / 2. Author to whom correspondence should be addressed / Received November 24, 1994
Summary
Xylem cavitation and sap flow rates, stomatal conductance and shoot water potential were observed in irrigated and drought-treated
saplings of Sitka spruce (Picea sitchensis (Bong.) Carr.), a drought-susceptible species, and Scots pine (Pinus sylvestris L.), a drought-resistant species. In Scots pine, cavitation rates increased as shoot water potential decreased below a threshold
of around –0.55 MPa. In Sitka spruce, cavitation rates were inversely related to shoot water potential in irrigated saplings
but not in drought-treated saplings. Sap flow rates declined sharply in both species as shoot water potential fell during
the drought treatment. Thus sap flow rate was positively associated with cavitation rate in Scots pine but not in Sitka spruce.
Three days after the drought treatment ended, shoot water potentials, stomatal conductances and sap flow rates in both species
regained values observed before the drought treatment. In Sitka spruce, stem relative water content also returned to a value
close to that observed before the drought treatment. Even 2 weeks after the end of the drought treatment, however, shoot relative
water content of Scots pine remained significantly lower than it had been before the drought treatment.
Keywords:
drought, Picea sitchensis, Pinus sylvestris, sap flow rates, stem relative water content, stomatal conductance, threshold water potential, ultrasonic acoustic emissions.
