The effect of soil temperature on the bud phenology, chlorophyll fluorescence, carbohydrate content and cold hardiness of Norway spruce seedlings.

The effects of soil temperature on the shoot phenology, carbohydrate dynamics, chlorophyll fluorescence and cold hardiness of 4-year-old Norway spruce seedlings (Picea abies L. Karst.) were studied. The experiment was carried out under controlled conditions in the Joensuu dasotrons. Air conditions were similar but soil temperatures differed by treatments (9, 13, 18 and 21 degrees C) during the second growing period in the dasotrons. The after-effects of the treatments were investigated during the third growing period following the treatments. Low soil temperature increased the starch content of needles and delayed the loss of starch at the end of the growing season. The photochemical efficiency (F(v)/F(m)) of the PSII of the current-year needles was reduced at the lowest soil temperature. The cold hardiness of needles correlated with the soluble sugar content. The differences in soil temperature had no effect on the timing of bud burst. No after-effects from the treatments were observed during the third growing period in the dasotrons.