influence of night temperature under declining photoperiod on bud initiation in black spruce seedlings

The effect of night temperature on the speed of bud initiation in black spruce (Piceamariana (Mill.) B.S.P.) container seedlings was studied. Day lengths were progressively shortened in plant growth chambers to simulate the natural day-length decline that occurs in the fall at latitude 48°N. During the period of day-length decline a constant 26 °C day temperature was maintained, while night temperatures of 5, 7.5, 10, 14, 18, 22, 24, or 26 °C were imposed. When the night temperature was 10-24 °C, first signs of bud initiation were observed in 12-15 days, while 100% bud initiation was attained in 15-22 days. When the night temperature was 5, 7.5, or 26 °C, first bud initiation was observed in 15-22 days, while 100% bud initiation was not attained until 40 days.