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Title:	Short-day treatment alters Douglas-fir seedling dehardening and transplant root proliferation at varying rhizosphere temperatures
Author(s):	Jacobs, Douglass F.; Davis, Anthony S.; Wilson, BArrett C.; Dumroese, R. Kasten; Goodman, Rosa C.; Salifu, K. Francis
Date:	2008
Source:	Can. J. For. Res., Vol. 38: 1526-1535
Description:	We tested effects of shortened day length during nursery culture on Douglis-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) seedling development at dormancy release. Seedlings from a 42 N source were grown either under ambient photoperiods (long-day (LD)) or with a 28 day period of 9 h light: 15 h dark photoperiods (short-day temperatures was investigated via electrolyte leakage at nine test temperatures ranging from 2 to -40 C. New root growth was assessed with rhizosphere temperatures of 10, 15, 20 and 25 C. From 2 to -13 C, there was no difference between treatments in cold hardiness. However, at or below -18 C, LD seedlings exhibited higher indices of damage than SD seedlings. The LT₅₀ (temperature at which 50% cell electrolyte leakage occurred) was consistently lower for SD than LD seedlings. Rhizosphere temperature differentially influenced new root proliferation: LD seedlings had greater new root production than SD seedlings at 20 C, whereas the opposite response was detected at 10 C. Our results confirm photoperiod sensitivity of Douglas-fir sources from relatively low (i.e., < 45 N) latitudes. Increased spring cold hardiness and greater rooting at lower rhizosphere temperatures may improve field performance potential of SD-treated seedlings.
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