© 1999 Heron Publishing—Victoria, Canada
Freezing cycles enhance winter injury in Picea rubens
Anne E. Lund (1) and William H. Livingston (2, 3)
1. Department of Biological Sciences, Colby College, Waterville, ME 04901, USA / 2. University of Maine, Department of Forest Ecosystem Science, 5755 Nutting Hall, Orono, ME 04469, USA / 3. Author to whom correspondence should be addressed (livingst@umenfa.maine.edu) / Received February 17, 1998
Summary
We examined changes in chlorophyll absorbency in red spruce (Picea rubens Sarg.) foliage in response to simulated freezing cycles. Current-year branch tips were collected from 16 trees on January
8, January 20, February 8 and February 26, 1996. Tissue was subjected to freezing cycle treatments with a minimum of –35 °C
and a maximum of 3 °C for a one-cycle treatment, and –9, –6, –3, 0 or 3 °C for four-cycle treatments. Samples were frozen
at a rate of 5 °C h–1, and warmed at 12 to 15 °C h–1. Controls were held at –9 °C. Temperatures during the three-day periods preceding each sample date averaged –18, 4.7, –9.6
and 3.7 °C, respectively. On January 8, treated trees showed no significant (P > 0.1) increase in the breakdown of chlorophyll, as measured by the ratio of chlorophyll a absorbency (435 nm) to phaeophytin
a absorbency (415 nm), compared with control branch tips. On later sampling dates, seven trees consistently exhibited needle
reddening and nine exhibited few symptoms (< 10% of total needle surface reddened) after four-cycle treatments. On February
26, chlorophyll degradation in trees with needle reddening differed (P < 0.05) from the control by 26, 26, 16, 14 and 15% for the 3, 0, –3, –6 and –9 °C maxima, respectively. No detectable chlorophyll
degradation occurred after a one-cycle treatment in any trees on any sampling date. Freezing cycles with sub-zero maxima and
a –35 °C minimum enhanced winter injury in red spruce after a midwinter thaw had rendered the trees susceptible to freezing
damage.
Keywords:
cold hardiness, cold tolerance, forest decline, freezing tolerance, frost hardiness, red spruce, tree decline, winter thaw.
