Premature dehardening in Vaccinium myrtillus during a mild winter: A cause for winter dieback?
Functional Ecology: 1996 10:724-732
1. During a 5 degrees C warmer-than-average winter in north-eastern Sweden, Vaccinium myrtillus suffered lethal injuries. During the following, equally mild winter a retrospective investigation was carried out to elucidate the underlying mechanisms. 2. Rehydrated shoots were most cold tolerant when tested in early winter, intermediate tolerant in mid-winter and least tolerant in late winter. 3. Solute content of shoots decreased considerably over winter. 4. It is suggested that the damage is caused by the progressive respiratory loss of cryoprotective sugars. 5. Based on gas exchange it was estimated that initial carbohydrate reserves would have lasted 4 months only if tissue water content had remained high. 6. As snow cover was thin and weather often clear, shoots were dehydrated which improved their cold tolerance 5-10 degrees C. This may explain why dieback did not occur during this winter, but during the preceding winter when misty and rainy days were twice as frequent. 7. In addition to long-term dehardening, a short-term dehardening was described following transition to constant non-freezing temperatures, which was similar to a phenomenon observed in Picea abies. 8. Chlorophyll fluorescence as a tool for probing freezing damage was evaluated. This revealed a high capacity for recovery from initial damage.
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