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Articles

Effects of Quality, Intensity, and Duration of Light Breaks during a Long Night on Dormancy in Blue Spruce (Picea pungens Engelm.) Seedlings ¹

^a Department of Forestry, Michigan State University, East Lansing, Michigan 48824

Blue spruce (Picea pungens Engelm.) seedlings grow continuously when exposed to photoperiods exceeding 16 hours and enter dormancy within 4 weeks under photoperiods of 12 hours or less. Dormancy was prevented under 12-hour photoperiods by 2-hour light breaks of red light (1.70 µw/cm² at 650 nm) or high intensity white light (2,164.29 µw/cm² at 400 to 800 nm) given in the middle of the 12-hour night, and by continuous low intensity white light (204.76 µw/cm² at 400 to 800 nm). Two-hour light breaks of far red light (1.80 µw/cm² at 730 nm), red light followed by far red light, or low intensity white light were not effective in delaying dormancy. The results imply that the phytochrome system mediates the photoperiodic control of dormancy in blue spruce seedlings. The similarity of results obtained using the low intensity, long duration as against the high intensity, short duration light treatments suggests that the law of reciprocity applies in this response.

¹ Michigan Agriculture Experiment Station Journal Article No. 7824.