INFLUENCE OF CULTURAL-PRACTICES ON THE RELATIONSHIP BETWEEN FROST TOLERANCE AND WATER-CONTENT OF CONTAINERIZED BLACK SPRUCE, WHITE SPRUCE, AND JACK PINE-SEEDLINGS

Two experiments were performed to study how cultural practices influenced the relationship between frost tolerance and water content of black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), and jack pine (Pinus banksiana Lamb.) seedlings. In the first experiment, first-year black spruce seedlings were subjected to 14-d mid-August treatments of short days of 8 h or to natural day length, during which time seedlings were either irrigated or not. In the second experiment, first-year white spruce, black spruce, and jack pine seedlings were fertilized at two levels, normal or double, during the growing season. In the fall, we followed the evolution of frost tolerance, water content (dry weight to fresh weight ratio), height and diameter growth, bud formation, and mineral concentrations of shoots and roots. In the first experiment, short days accelerated frost acclimation, drop in water content, and bud formation. Short days with no irrigation triggered the cessation of height growth. In the second experiment, normal fertilization slightly improved frost tolerance in white spruce. Diameter growth (except for white spruce) and bud formation were enhanced by high nitrogen concentration, whereas no significant effect of fertilization could be found on height growth and water content. In both experiments, the relationship between frost tolerance and water content was independent of treatments and indicated that nontolerant seedlings (lethal temperature for 50% of the seedlings > -10-degrees-C) had dry weight to fresh weight ratios of less than 30% for the three species. Thus, this rapid method of evaluating frost tolerance could be useful to seedling producers in eastern Canada and might be applicable to other species in other regions as well.