© 1991 Heron Publishing—Victoria, Canada
In situ experimental freezing produces symptoms of winter injury in red spruce foliage
G. R. Strimbeck, D. R. Vann and A. H. Johnson
Department of Geology, University of Pennsylvania, Philadelphia, PA 19104, USA / Received March 15, 1991
Summary
Two mechanisms have been proposed to explain winter injury to needles of red spruce (Picea rubens Sarg.): (1) desiccation, which is characterized by net loss of foliar water from the needle to the environment, with cell
injury resulting from dehydration; and (2) freezing, which is characterized by direct injury to cells resulting from intracellular
or extracellular ice formation during exposure to low temperature. To compare the separate and combined effects of freezing
and desiccation, branches of a mature red spruce at 1160 m were (a) experimentally frozen in situ to –50 °C; (b) cut and tied
in their original orientation and allowed to desiccate passively; or (c) both frozen in situ and cut and tied in their original
orientation. Needle water content, electrolyte leakage (an index of cell injury), and needle color were monitored for 60 days
after treatment. Freezing resulted in immediate increases in electrolyte leakage, rapid water loss, and reddening necrosis
of needles similar to that of naturally injured needles. Cutting resulted in more gradual water loss, no significant changes
in electrolyte loss until severe desiccation had occurred, and a change in the color of the needles to a dull green. Because
freezing produced reddening necrosis, a key symptom of winter injury, whereas desiccation did not, we conclude that freezing
is probably the primary cause of winter injury in red spruce, and that desiccation is a secondary effect.
