© 2000 Heron Publishing—Victoria, Canada
Effects of xylem cavitation and freezing injury on dieback of yellow birch (Betula alleghaniensis) in relation to a simulated winter thaw
X. B. Zhu (1), R. M. Cox (2, 3) and P. A. Arp (1)
1. Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton, NB E3B 6C2, Canada / 2. Natural Resources Canada, Canadian Forest Service—Atlantic Forestry Centre, Fredericton, NB E3B 5P7, Canada / 3. Author to whom correspondence should be addressed (rcox@nrcan.gc.ca) / Received August 11, 1999
Summary
Shoot dieback, shoot growth, stem xylem cavitation, stem and root freezing injury, and root pressure were measured in 2-year-old,
cold-hardened, potted yellow birch (Betula alleghaniensis Britt.) seedlings that had been subjected to a simulated winter thaw for 0, 5, 10, 19 or 27 days followed by 10 weeks at
–10 °C. Stem xylem cavitation was determined as percent loss of hydraulic conductivity. Stem freezing injury was measured
as electrolyte leakage (EL). Root freezing injury was determined by EL and by triphenyl tetrazolium chloride (TTC) reduction.
Thaw duration was significantly correlated with dieback, new shoot growth, stem xylem cavitation, stem and root freezing damage,
and root pressure (P < 0.05). In particular, shoot dieback was positively correlated with stem xylem cavitation (P < 0.001), residual stem xylem cavitation (P < 0.01) and root freezing injury (P < 0.010), but only weakly correlated with stem freezing damage (P < 0.05). In roots, freezing damage was negatively correlated with root pressure (P < 0.05), which, in turn, was negatively correlated with residual stem xylem cavitation after root pressure development. In
stems, there was no correlation between freezing damage and xylem cavitation. We conclude that long periods of winter thaw
followed by freezing resulted in freezing injury to roots concomitant with a reduction in root pressures, leading to poor
recovery from freezing-induced xylem embolism.
Keywords:
dieback, new shoot growth, residual xylem embolism, thaw duration, stem xylem cavitation.
