| Abstract: | The frost hardiness of non-juvenile Norway spruce Picea abies (L.) Karst.] populations growing in northern Sweden (63°54' N) was monitored during 1996-1997. The investigated progenies originated from 12 natural populations and six seed orchards located between 58° N and 68° N in Sweden. Frost hardiness of needles was assessed by measuring chlorophyll fluorescence and electrolyte leakage after freezing. The loss of frost hardiness in 1-yr-old needles during spring occurred slightly earlier in populations originating north of 63°30' N than in those originating further south. Dehardening was slightly delayed in selected populations compared with natural populations of similar origin. The level of frost hardiness during autumn was higher in populations originating north of 63°30' N than in those originating south of this latitude, but there were no clear differences in frost hardiness between selected and natural populations of similar origin. The results are discussed in relation to climatic factors and inherent growth rhythms. |
