FREEZING DEHYDRATION DAMAGES ROOTS OF CONTAINERIZED SCOTS PINE (PINUS-SYLVESTRIS) SEEDLINGS OVERWINTERING UNDER SUB-ARCTIC CONDITIONS

The survival of conifer roots under winter conditions is not well unde rstood. The effect of long-lasting freezing at extremely low temperatu res on the survival of the roots of Scots pine (Pinus sylvestris L.) s eedlings from a timberline seed source was studied. One-year-old conta inerized seedlings were kept for 4 months under winter conditions typi cal of the subarctic region. The freezing treatment was accelerated by preventing snow accumulation on half of the seedlings. The proportion of living root tissue and the amount of sugars (glucose, fructose, an d sucrose) and starch in the needles and roots were measured at weekly intervals. The temperature within the growth medium without snow cove r fell on a number of occasions to -30 degrees C. The lowest temperatu re recorded within the snow-covered growth medium was -20 degrees C. T he sugar content increased faster and to a higher level in the seedlin gs without snow cover, but it did not affect root survival. The propor tion of living root tissue without a cover of snow decreased by 80% by the end of December, and the roots were completely injured by the end of February. There was only a slight decrease in the proportion of li ving roots among seedlings covered by snow. The reduced root survival was not directly related to exposure to the lowest freezing temperatur es; instead, it was manifested some weeks after exposure. This suggest s that dehydration resulting from prolonged severe freezing caused roo t damage. The presence of a cover of snow reduces subzero temperature extremes and the severity of dehydration; together, these result in en hanced root survival.