Abstract
Changes in the freezing tolerance for Silene acaulis L., a subarctic and arctic species of circumpolar distribution, were examined to understand the extent of cold hardening and dehardening that occurs seasonally and with changes in plant phenology. Shoots of whole plants collected on a mountain ridge near Tromsø, Norway (69° N, 700 m above sea level) were frozen under controlled conditions at cooling rates of 3 to 4°C h-1. The extent of freezing-induced injury was examined both by chlorophyll fluorescence and by visual inspection with a microscope. A freezing tolerance level of -30°C was observed in mid-winter, based on a 50% lethal point for freezing injury. Loss of cold hardiness was substantial in mid-summer, with freezing tolerance of -8·5 to -9°C observed in mid-July. Plants still covered by snow in mid-July had a freezing tolerance of -12·5 to -13°C. The maintenance of a basic level of freezing tolerance throughout the summer may be adaptive in the northern latitude-regions because of the occurrence of episodic frosts during the growing season.
Published Version
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