Growth and Dormancy in Norway Spruce Ecotypes

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Abstract
Height and radial growth of spruce in years n+ 1, n+ 2, and n+ 3 as affected by photoperiod and temperature in year n have been studied in controlled environments and in the field.In agreement with common opinion apical shoot growth in year n+ 1 was strongly dependent on the temperature conditions prevailing in the period following budset in year n. This was found mainly to be a direct effect upon the differentiation of the shoot and needle primordia for next year's growth. A similar, although less pronounced effect, was found also on radial growth, possibly an indirect effect elicited through the effect on apical growth.A rather wide temperature optimum of 18 to 24°C was found in three Norwegian ecotypes and a somewhat lower optimum (15 to 18 C) in an Austrian high altitude ecotype. The shorter the bud differentiation period, the higher was the temperature optimum in all ecotypes (heat sum effect). Photoperiod which is the main factor controlling the time of budset, thus had a great after‐effect.The after‐effect was strongly modified by photoperiod and to a lesser extent also by temperature in the current growing season. It is concluded that in second‐year or older spruce plants the important effect of photoperiod in the current growing season is to control quantitatively and qualitatively the amount of secondary (lammas) shoot formation, and to modify shoot extension in the main growth flush. Longer photoperiods were needed for continuation or resumption of growth in second‐year plants than for maintenance of uninterrupted growth in first‐year seedlings.Delayed flushing was observed in plants maturing at high temperatures, indicating that these plants had entered a deeper state of dormancy than those maturing at lower temperatures.Also in years n+ 2 and n+ 3 apical and radical growth was significantly related to photoperiod and temperature conditions in year n. This effect gradually became an indirect one through the effects on general plant size (leaf and root area).The results are discussed in the light of previous work in the field.