摘要 : Chlorophyll fluorescence measurements were performed on the foliage of 3-year-old (1(1)/2 + 1(1)/2) nursery-grown Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings after exposure to controlled freezing temperatures, in ... 展开 Chlorophyll fluorescence measurements were performed on the foliage of 3-year-old (1(1)/2 + 1(1)/2) nursery-grown Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings after exposure to controlled freezing temperatures, in the laboratory, to assess low temperature tolerance. The seedlings were propagated in an Irish nursery and lifted at monthly intervals overwinter 1999 and 1999-2000. Excised shoots from first-order laterals were frozen, in the dark. After freezing, needles were immediately assessed using chlorophyll fluorescence. The excised shoots were then maintained under controlled conditions for 14 days and visually assessed for needle damage. The chlorophyll fluorescence parameter, F-v/F-m, accurately predicted cold hardiness and was linearly related to visual needle damage and short-term survival. An equation was constructed using F-v/F-m data for determining the LT50, that is, the freeze temperature causing 50% seedling damage. The predictions of F.LT50 (fluorescence-based empirical determination of LT50) have been tested over two seasons (i.e., against a second independent data set) with variability between 0 and 1.8degreesC of visual estimates, though predictions were often less than or equal to 1.1 degreesC of the visual assessment. This approach provided a simple, rapid and accurate prediction of cold tolerance, under climatic conditions where in situ measurements are unreliable. The method can be used to predict if Douglas-fir seedlings have developed sufficient tolerance for lifting to the cold-store, or for planting. 收起