Photoperiodic reactions in conifer species

In Picea abies seedlings the critical night length for bud-set was determined for provenances from different latitudes, longitudes and altitudes within the natural range of the species. The clinal variation of this character was demonstrated. Inheritance studies indicated that this character is controlled by many genes with predominantly additive effects. In seedlings of Pinus sylvestris and Pinus contorta, growth cessation and bud-set took place in all light regimes, thus, even under continuous illumination. A photoperiodic optimum for height growth was determined. The photoperiodic influence on such characters as recurrent flushing of shoots, needle growth, dry matter production and frost resistance was demonstrated for northern and southern populations of the two Pinus species. Shorter nights were needed to induce a particular photoperiodic response in the northern populations as compared with those from the south. The importance of reliable phenological characters for assessing frost hardiness in provenance and progeny trials by means of early tests, is discussed.