ASSESSING COLD TOLERANCE IN PICEA USING CHLOROPHYLL FLUORESCENCE

Chlorophyll fluorescence measurements were performed on field-collected red spruce foliage exposed to controlled freezing temperatures to determine the utility of chlorophyll fluorescence kinetics in assessing low temperature tolerance. No significant decreases in fluorescence relative to unfrozen control foliage were observed at progressively lower temperatures until a critical temperature was reached, whereupon rapid, irreversible decreases in fluorescence occurred. Weekly comparisons between cold tolerance estimates derived using chlorophyll fluorescence inflection point temperatures and foliar visual LT20 (temperature at which 20% of foliage exhibited necrosis) estimates were also made throughout the winter of 1991-1992. No significant differences in weekly cold tolerance estimates between the two methods were evident. The weekly absolute difference in mean cold tolerance using the two methods was 3.0-degrees-C. These results indicate that chlorophyll fluorescence is a rapid, consistent, and reproducible method of determining low temperature tolerance of spruce foliage.