Effect of supplemental light intensity on white spruce, Engelmann spruce, and mountain hemlock seedlings grown under an extended photoperiod

Abstract

Piceaglauca (Moench) Voss, Piceaengelmannii Parry and Tsugamertensiana (Bong.) Carr. were grown in an unheated "shelterhouse" container nursery, with a high pressure sodium vapour lamp providing a 19-h photoperiod and light intensities of 1600, 800, 400, 200, and 100 lx. The control seedlings received natural daylight and photoperiod. None of the light intensities effectively prevented terminal bud formation in the first two species while no terminal buds were formed at the 1600 lx level in the third one. Higher light intensities delayed the bud forming process in the first and third species, produced significant differences in the number of stem units of the first two, and resulted in larger mean stem unit lengths of the last two species. The longest seedling shoots of all three species were grown under light intensities of 800, 100, and 400 lx, respectively. There were no significant differences in seedling shoot weight, root weight, and root collar diameter among the five light intensity levels used to extend the photoperiod in the first growing season. Light intensity had little effect on 2-year shoot growth of all three species.