EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON THE TIMING OF BUD BURST IN NORWAY SPRUCE (PICEA-ABIES)

We examined the effects of several photoperiod and temperature regimes imposed during the winter-spring period on the timing of bud burst in rooted cuttings of Norway spruce (Picea abies (L.) Karst.) grown in a greenhouse in Finland. The treatments were initiated in November and December after the cuttings had been exposed to natural chilling and f reezing events. Irrespective of the treatments applied, time to bud bu rst decreased with increased duration of previous exposure to natural chilling and freezing events. Fluctuating day/night temperatures and c ontinuous lengthening of the photoperiod hastened bud burst. Shortenin g the photoperiod delayed bud burst, suggesting that little or no onto genetic development toward bud burst takes place during mild periods b efore the winter solstice. In the case of climatic warming, this pheno menon may prevent the premature onset of growth that has been predicte d by computer simulations with models that only consider temperature r egulation of bud burst.