SEASONAL-CHANGES IN CHLOROPHYLL FLUORESCENCE OF WHITE SPRUCE SEEDLINGS FROM DIFFERENT LATITUDES IN RELATION TO GAS-EXCHANGE AND WINTER STORABILITY

Variable chlorophyll fluorescence (F-var) was investigated as a tool i n the detection of distinct seasonal physiological changes in 1+0 inta ct white spruce seedlings. The loss of the characteristic F-var peak ( Fp) between 0.8 and 1.0 s after illumination of dark adapted seedlings is an indication of regulation of photosynthetic activity in August. The peak represents excess photochemical water-splitting of photosyste m II. We interpret its loss as a physiological indicator of the proces s of dormancy induction. Three dimensional (i.e. X[0-300 s], Y[rfu], Z [time of year] axis) F-var curves of non-stressed seedlings measured o ver 300 s followed a three phase change over the growing season. In ac tively growing seedlings, the portion of the Kautsky induction curve b etween 60 and 300 s was 0.4 relative fluorescence units (rfu) in north ern (i.e. >56 degrees latitude) seedlots and 0.6 in the southern (i.e. <56 degrees latitude) range seedlot from August until early September . About mid-September curve features between 60 and 300 s decreased sh arply to approximately zero (rfu) by October. Freeze test data indicat ed seedlings became frost hardy during this time. The third, or inacti ve phase was seen as flat line from 40 to 100 s. The portion of the cu rve after 100 s was responsive to short term temperature changes. Whit e spruce seedlots of northern and southern B.C. latitudes having curve fluorescence peak (F-p) values at about 1 s of 0.6, and 0.8 (rfu) res pectively, plus curve minimum (F-min) values at about 60 a which do no t decrease further over a 2-3 week period represent stock which can sa fely be lifted for cold storage. The F-var. attribute at 5 s after the actinic light is turned on (F-5s) correlates well with net photosynth esis (r(2) = 0.61) during the growing season.