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Konttinen, K., Luoranen, J. and Rikala, R. 2007. Growth and Frost Hardening of Picea abies Seedlings after Various Night Length Treatments.   Baltic Forestry 13 (2): 140 - 148

We studied the effects of varying night length (NL: 16 h, 12 h or 10 h and ambient as control) treatments of three weeks duration on the morphology, shoot water content (WC) and frost hardiness (FH) of first-year Norway spruce (Picea abies (L.) Karst.) seedlings of northern (64° 40‘) and southern (60 ° 40‘) Finnish origins, and of first- and second-year Norway spruce seedlings of local origin at a nursery in Central Finland (62° 38‘). We also studied the height growth of the seedlings after planting. NL was negatively associated with the increment of stem diameter and root dry mass of seedlings. The NL treatments increased FH from 4 to 7°C compared with control seedlings, but differences between NL treatments were small. No consistent relationship between WC and FH was found. NL treatments had only a minor effect on seedling height growth after planting. In conclusion, the shorter (10-12 h) night is recommended for use in a blackout treatment.

Key words: frost hardening, night length, Norway spruce, origin, Picea abies, photoperiod, short-day treatment