Norway Spruce (Picea abies [L.] Karst.) Provenance Variation in Autumn Cold Hardiness: Adaptation or Acclimation?
We tested autumn frost hardiness in three Norway spruce (Picea abies [L.] Karst.) provenances originating from different altitudes at two trial plots in Slovakia (Vel'ký Lom at 450 m a.s.l., Mútne-Zákamenné at 1,250 m a.s.l.) in a spinoff experiment of the IUFRO 1964/68 Inventory Provenance Experiment with Norway spruce. Two approaches were used to assess hardiness: the electrolyte-leakage method based on artificial freezing, and measurements of chlorophyll a fluorescence parameters. The frost injury index at -20°C differed between provenances, with a significant provenance-by-plot interaction. In material from the lower-altitude Vel'ký Lom trial plot, the high-elevation TANAP provenance exhibited much lower frost injury than the middle-elevation Habovka and low-elevation Beňuš provenances. In material from the high-altitude Mútne-Zákamenné trial plot, all three tested provenances showed approximately the same degree of frost injury. At -80°C no differences between provenances were observed, and the trees growing at the high-elevation site exhibited lower average frost injury than the trees at Vel'ký Lom. Most parameters of the kinetics of chlorophyll a fluorescence followed the same trends as frost injury, and differed significantly between plots. We suggest that the observed differences resulted from acclimation of trees to the conditions of the trial plots rather than from adaptation through natural selection.