Environmental Control of Cold Acclimation in Douglas Fir During Germination, Active Growth, and Rest

Abstract

Controlled-environment experiments were conducted on Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings during their 1st year. Hardiness of foliage was assessed by visually estimating injury after freezing tests.Germinants (1 week) were unable to attain any freezing tolerance under 8-h days at 2 °C even after 9 weeks but were killed whenever ice formed. Their ability to supercool increased by 5 °C during this treatment. However, seedlings older than 3 weeks (1 to 2 cm of epicotyl) could develop true hardiness under the influence of either short days (less effective) or low positive temperatures, independently of lignification, bud setting, or entry into rest. Ability to acclimate increased gradually with age and was inversely related to growth and maturation, apparently because the latter processes had higher temperature optima. Photoperiod affected growth and bud formation only above about 15 °C but influenced hardiness at 1 °C. The optimum photoperiod for inducing hardiness was longer at low light intensities than at high ones, presumably because of a minimum requirement for photosynthesis.Interruption of the long inductive dark period with 15 min of red light (650 nm) caused a small decrease in hardiness and bud set and an increase in growth. This effect was not reversed, but was enhanced by an isoenergetic burst of far-red (FR) light immediately after. FR interruptions alone had no effect. Night frosts (−7 °C) caused significant dehydration and rapidly increased hardiness only if both the warm, short day and chilling "stages" had been supplied first and the daily supply of light continued.

Frost tolerance and hardening capacity during the germination and early developmental stages of four white spruce (Picea glauca) provenances

“…Neither of these studies, however, indicates the developmental stage of seedlings at the beginning of the treatment or when they were freeze tested. Finally, Timmis and Worrall (1975) also reported that 7-week-old seedlings (2-cm epicotyl) of Pseudotsuga menziesii reacted to low temperature treatments by increasing their frost tolerance and that 1-week-old seedlings submitted to low-temperature treatments also reacted in the same way, but not until their epicotyl had started elongating.…”

“…According to Timmis and Worrall (1975), 3-(1 cm long epicotyl) and 7-week-old (2 cm long epicotyl) seedlings of Pseudotsuga menziesii (Mirb.) Franco reacted to a lowtemperature -short-photoperiod treatment by increasing their frost tolerance, and the degree of response increased with age.…”

Daylength, temperature and fertilization effects on desiccation resistance, cold hardiness and root growth potential of Picea mariana seedlings

“…It also may have been a response to desiccation [26], as desiccated tissues are more cold hardy than fully hydrated ones [28]. While seedlings exposed to colder temperatures during the early stages of hardening can cold harden more quickly, it has been shown elsewhere that premature exposure to cold temperatures can prevent the attainment of maximal cold hardiness [12,36].…”

Effect of frost nights and day and night temperature during dormancy induction on frost hardiness, tolerance to cold storage and bud burst in seedlings of Norway spruce

“…), although this practice has not been studied explicitly (van den Driessche 1970;Aronsson 1975;Jonsson et al 1981;Johnsen 1989a). Occurrence of frost nights during the dormancy induction period has been shown to induce deeper hardiness in both angiosperms (Junttila and Kaurin 1990) and conifers (Timmis and Worral 1975;Greer and Warrington 1982;Hawkins 1993;Silim and Lavender 1994). The impact of frost nights as they might occur in nature during early autumn has, to our knowledge, not been studied experimentally using controlled freezing chambers in Norway spruce.…”