Sammendrag
Subalpine fir (Abies lasiocarpa (Hooker) Nuttall), which is native to western North America,
is of considerable interest for Christmas tree production in northern Europe. Seedlings are usually
grown from seeds under combined nursery greenhouse/outdoors conditions, but commonly show
early growth cessation in the nursery, resulting in small plants for field transplanting. This increases
the production time and makes the seedlings vulnerable to stressors at the planting site. Day extension
with far-red (FR) light was shown to enhance elongation and delay bud set in seedlings of some woody
species, but such information is limited for Abies. Here, we investigated the effects of day extension
with FR, red (R), different R:FR-ratios or blue (B) light from light emitting diodes on subalpine fir
seedlings grown at different temperatures. Day extension with FR or combined R-FR light, in contrast
to R or B light, increased shoot elongation significantly as compared to short days without day
extension, often with more growth at 18 ◦C than 24 ◦C. The FR treatments delayed terminal bud
development, although bud set was not completely prevented. These results demonstrate that larger
seedlings of subalpine fir seedlings for Christmas tree production can be obtained by employing day
extension with FR or combined R:FR light, preferably under cool temperature.
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