© 2003 Heron Publishing—Victoria, Canada
Characterizing the frost sensitivity of black spruce photosynthesis during cold acclimation
D. Gaumont-Guay (1, 2, 3), H. A. Margolis (1), F. J. Bigras (4) and F. Raulier (4)
1. Faculté de foresterie et de géomatique, Université Laval, Québec, Québec G1K 7P4, Canada / 2. Faculty of Agricultural Sciences, University of British Columbia, 266B-2357 Main Mall, Vancouver, BC V6T 1Z4, Canada / 3. Author to whom correspondence should be addressed (dgguay@interchange.ubc.ca) / 4. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du P.E.P.S., P.O. Box 3800, Sainte-Foy,
Québec G1V 4C7, Canada / Received February 27, 2002; accepted July 27, 2002; published online March 3, 2003
Summary
We used photosynthetic light response curves to measure and model the responses of two provenances of 3-year-old black spruce
(Picea mariana (Mill.) BSP) seedlings to severe artificial frost treatments applied at 2-week intervals during cold acclimation. Black spruce
seedlings responded to cold acclimation with long-term suppression of photosynthetic capacity (Amax) and apparent quantum-use efficiency (α′). Short-term reductions in both photosynthetic parameters following frost treatments
were dependent on the extent of cold acclimation of the seedlings and the severity of the frost treatments. Large reductions
in Amax in response to the frost treatments were observed in seedlings that had undergone little cold acclimation and these reductions
were associated with an irreversible reduction in α′. Such seedlings recovered only partially during the subsequent 23 days,
whereas seedlings in most other treatments showed complete recovery of Amax after 13 days. The impact of frost treatments on Amax and α′ did not vary with seedling provenance. We propose an algorithm that predicts the combined effects of cold acclimation
and severe freezing temperatures on the extent of the suppression of Amax during autumn. The algorithm is based on (1) the maximum Amax observed during the growing season, (2) the accumulation of cold degree-days, based on a minimum nocturnal temperature <
5 °C, and (3) the severity of freezing temperatures during autumn. The parameters developed in the algorithm showed that cold
acclimation of black spruce seedlings had a greater impact on the reduction of Amax in autumn than did the severe frost treatments. Mean Amax of seedlings subjected to artificial frosts showed a strong correlation with values predicted by the algorithm (r2 = 0.91).
Keywords:
boreal forest, conifer, freezing temperatures, hardening, model, Picea mariana, photosynthetic capacity, photosynthetic efficiency.
