Bud development in Sitka spruce. I. Annual growth cycle of vegetative buds and shoots

Abstract

Vegetative apices of Picea sitchensis (Bong.) Carr. were studied throughout the annual growth cycle. Apices became mitotically active late in March and the shoot axis and leaf primordia elongated causing the bud to swell. New axillary apices were initiated in mid-April and the terminal apex and new axillary apices initiated bud scales until early in July. Vegetative bud burst occurred early in June and shoot elongation was completed by mid-July. The end of shoot elongation coincided with the onset of leaf initiation. The change from bud-scale to leaf initiation was characterized by a period of increased mitotic activity and rapid apical growth. About half of the final number of leaves were initiated during the early period of rapid leaf initiation. The remaining leaf primordia were initiated more slowly over the next 3 mo. Buds became dormant by mid-Nov.