Effects of xylem cavitation and freezing injury on dieback of yellow birch (Betula alleghaniensis) in relation to a simulated winter thaw.

摘要

Two-year-old, cold-hardened, potted yellow birch (Betula alleghaniensis) seedlings were subjected to a simulated winter thaw for 0, 5, 10, 19 or 27 days followed by 10 weeks at -10deg C. Stem xylem cavitation was determined as percent loss of hydraulicconductivity. 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, stemxylem cavitation, stem and root freezing damage, and root pressure. Shoot dieback was positively correlated with stem xylem cavitation, residual stem xylem cavitation and root freezing injury, but only weakly correlated with stem freezing damage. In roots, freezing damage was negatively correlated with root pressure, 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. It is concluded that long periods of winter thawing 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.