Light inhibition of rooting in Norway spruce (Picea abies) cuttings

Stem cuttings from 3-year-old seedlings of Picea abies L. (Karst.) (Norway spruce) were rooted in tap water in a growth chamber. The effect of two levels of irradiance given to either the upper two thirds of the cuttings or to the whole cutting was investigated. When only the upper two thirds of the cuttings were irradiated, the number of cuttings which rooted was lower at the higher irradiance level (40 W m−2) as compared with the number rooting at the lower irradiance level (8 W m−2). Rooting was inhibited almost completely at either of the irradiances if the base of the cutting was also irradiated.