Chlorophyll fluorescence and variations in tissue cold hardiness in response to freezing stress in Douglas-fir seedlings
Source: New Forests, Volume 23, Number 2, March 2002 , pp. 81-96(16)
Abstract:Two-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings from two seed lots were exposed to controlled freezing temperatures every 4 weeks from October 1993 through April 1994. Freezing effects were assessed by measuring chlorophyll fluorescence emissions 1 day after freezing and by evaluating damage to the bud, cambium, and needle tissues 7 days after freezing. Differences between the seed lots as well as changes in cold hardiness among the bud, cambium, and needle tissues were evident throughout the duration of the study. Tissue damage was higher with increased freezing stress. Severity of damage to each of the tissues varied seasonally. Chlorophyll fluorescence emissions were lower with higher freezing stress (except during November and December, when test temperatures were not low enough to significantly damage the seedlings) and showed a strong relationship with morphological assessments of freezing stress. The slope of the slow kinetics phase of the chlorophyll fluorescence curve tended to be less steep (i.e., quenching was reduced) with higher freezing stress. Nonfrozen chlorophyll fluorescence measurements showed no obvious relationship with LT_50for either seed lot. However, chlorophyll fluorescence measurements are useful for determining cold hardiness and resistance to stress, because they provide a rapid assessment of seedling vigor following exposure to freezing.
Document Type: Regular Paper
Publication date: March 1, 2002