CHLOROPHYLL FLUORESCENCE AS AN INDICATOR OF FROST HARDINESS IN WHITE SPRUCE SEEDLINGS FROM DIFFERENT LATITUDES

This study examined the utility of variable chlorophyll fluorescence ( F-var) to detect freezing damage in white spruce seedlings of four see dlots. Logistic regression analysis done for freezing tests in Septemb er showed that visible needle damage from freezing could be estimated by the F-var attributes F-o/I-ABS(r(2) = 0.94), F-p(r(2) = 0.98), F-v/ F-m(r(2) = 0.99),and F-t(r(2) = 0.86). The regression curves indicated that for all four fluorescence attributes, inflection points occurred between 10 and 20% visible needle damage. The lack of a relationship between fluorescence attributes and visible seedling needle damage in October through December is because the minimum temperature (-18 and - 24 degrees C respectively) applied was insufficient to cause needle da mage. Freezing-induced changes to F-var attributes can be detected whi ch also result in photosynthetic rate decreases when no visible needle damage, and even electrolyte conductivity changes are evident. F-var attribute differences due to freezing can be resolved to the seedlot l evel. The F-var curve feature manifested 5 seconds after dark-adapted seedlings have been exposed to light (F-5s) will estimate (r(2) = 0.76 ) photosynthetic rate after freezing.