DEHARDENING AND 2ND-YEAR GROWTH OF WHITE SPRUCE PROVENANCES IN RESPONSE TO DURATION OF LONG-NIGHT TREATMENTS

Long-night treatments (16 h) of 0 (control), 4, 8, 12, and 16 days dur ation were applied, in August 1994, to four provenances of 10-week-old white spruce (Picea glauca (Moench) Voss) seedlings. This was to dete rmine the shortest duration that would produce seedlings having accept able morphological and physiological characteristics for reforestation . The effects of these treatments and of the latitude of origin of see dlings on the course of dehardening and second-year growth were studie d Terminal bud burst, shoot and root dry mass accumulation, and frost tolerance were followed during the spring, and terminal shoot growth w as measured until August. Seedlings exposed to 0 (control) or 4 long n ights exhibited significant amounts of damage in the spring. This dama ge had occurred the previous fall or winter. Seedlings receiving 4 to 16 days of long-night treatments did not differ in timing of bud burst the following spring, while the most northern provenance flushed firs t (May 18) and the most southern flushed last, 4 days later. Seedlings subjected to 8, 12, and 16 long nights exhibited similar amounts of t erminal shoot growth, dry matter accumulation, and frost tolerance. Fr ost tolerance of the 8-, 12-, and 16-d treatments during dehardening w as unaffected by the latitude of origin of seedlings. Our results sugg est that under the experimental conditions used, an 8-d long-night tre atment applied in the fall would produce seedlings with the same morph ological and physiological characteristics in the spring as a 12- or 1 6-d treatment.