Dynamics of low-temperature acclimation in temperate and boreal conifer foliage in a mild winter climate
G. Richard Strimbeck (1, 2), Trygve D. Kjellsen (1), Paul G. Schaberg (3) and Paula F. Murakami (3)
1. Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway / 2. Corresponding author () / 3. Forest Service, U.S. Department of Agriculture, Northern Research Station, South Burlington, VT 05403, USA / Received March 8, 2008; accepted April 22, 2008; published online July 1, 2008
Summary
To provide baseline data for physiological studies of extreme low-temperature (LT) tolerance in boreal conifers, we profiled
LT stress responses, liquid nitrogen (LN2)-quench tolerance, and sugar concentrations in foliage of boreal–temperate species pairs in the genera Abies, Picea and Pinus, growing in an arboretum in a temperate oceanic climate from August 2006 through April 2007. The boreal species acclimated
more rapidly and deeply than the temperate species, acquiring LN2-quench tolerance by late November, despite unusually warm conditions throughout the autumn and early winter. Maximum LT tolerance
in the temperate species was in the –25 to –35 °C range, and was reached only after a period of freezing temperatures in late
January and February. During LT acclimation in the temperate species, sigmoid temperature–relative electrolyte leakage (REL)
curves shifted toward lower temperatures, whereas in boreal species there was both a temperature shift and a lowering of the
maximum REL until it fell below a threshold associated with irreversible injury. These differences may reflect differences
in mechanisms of LT acclimation and LT tolerance. The concentrations of total and individual sugars did not show a clear pattern
that could differentiate the boreal and temperate groups. Raffinose and, in three of the six species, stachyose showed the
closest association with LT tolerance. Sugar concentrations, principally sucrose, decreased during mild weather, perhaps because
of respiratory losses or phloem export, and increased after periods of freezing temperatures. Low-temperature acclimation
in boreal species appears to follow a rigid program that may affect their ability to avoid excessive respiratory losses in
the event of continued climate warming in boreal regions.
