Growth Response of White-Engelmann Spruce Provenances to Extended Photoperiod Using Continuous and Intermittent Light

Abstract

Four white-Engelmann spruce provenances (latitudes ca. 49–54 °N and elevations 430–1770 m) were grown outdoors in containers from seed at low elevation in southwest British Columbia (48°26′N). Five photoperiod treatments were applied: three combinations of intermittent light (150 ft-c (1600 lux)) through the dark period, viz. A 2 min light every 30 min; B 1 min light every 10 min; C 15 s light every 6 min, and D an 18-h photoperiod (natural day length extended by 150 ft-c (1600 lux) supplemental light), plus E a control (natural day length).All control-grown provenances, except the southern latitude – low-elevation source, formed terminal resting buds and ceased height growth early in the growing season. Light treatments delayed this event. The most effective treatment in terms of height growth and total plant weight was A, usually followed by D, C, B, and E. It is suggested that white and Engelmann spruce from northern latitudes and high elevations in British Columbia can be successfully propagated in southern coastal container nurseries if the photoperiod is extended.