Physiological changes in red spruce seedlings during a simulated winter thaw

Abstract

We evaluated net photosynthesis, respiration, leaf conductance, xylem pressure potential (XPP) and cold hardiness in red spruce (Picea rubens Sarg.) seedlings exposed to either a continuous thaw (CT) or a daytime thaw with freezing nights (FN) for 8 days during mid-winter. Physiological differences between CT and FN seedlings were evident for all measured parameters. However, the temporal expression of treatment differences varied among parameters. When compared to FN seedlings, CT seedlings had higher rates of respiration following 24 h of treatment, and a higher net photosynthetic rate, leaf conductance and XPP after 48 h of treatment. The CT seedlings were significantly less cold tolerant than the FN seedlings following 4 days of thaw, whereas FN seedlings did not deharden over the 8 days of treatment. Examination of temporal trends among thaw-associated changes in physiology suggested that, although greater carbon exchange occurred as stomatal conductance increased, the transition from negative to positive net photosynthesis was not the result of increases in conductance, but may have been associated with thaw-induced increases in XPP. Because thaw-associated changes in gas exchange and cold hardiness were offset in time, we conclude that, if changes in these processes are physiologically linked, the linkage is indirect.

Management for red spruce conservation in Québec: The importance of some physiological and ecological characteristics – A review

“…For example, the For personal use only. maximum frost tolerance of the current year's foliage is generally -30°C to -50°C (DeHayes et al 1990b;Perkins et al 1993;Strimbeck et al 1995;Schaberg et al 1996Schaberg et al , 2000b), compared to -50°C to -90°C for balsam fir (DeHayes et al 1990b, Strimbeck et al 1995, and -80°C for black spruce and white spruce (DeHayes 1992). This comparatively low frost tolerance would explain why the natural range of red spruce is generally confined to areas with an absolute minimum temperature above -40°C (Arris and Eagleson 1989).…”

“…For example, Schaberg et al (1996) noted that frost tolerance of seedlings strongly decreased (-47°C to about -33°C) after four to eight days of simulated winter thawing with temperatures above 0°C. Similar reductions in frost tolerance were observed by Strimbeck et al (1995) in mature trees.…”

Yellow-cedar and western redcedar ecophysiological response to fall, winter and early spring temperature conditions

“…1). Mid winter increases the photosynthetic rates of coniferous species occur when there are warm air temperature events [42,43,48,50].…”

Physiological and Environmental Causes of Freezing Injury in Red Spruce

“…There is also evidence that climatic perturbations, such as the frequency of winter thaws, have also increased in at least some locations in the northeastern U.S. (Strimbeck et al, 1995;Schaberg et al, 1996). Because red spruce grows in regions where air temperatures usually remain below O°C throughout the winter, extended thaws that allow melting and mobilization of water in the plant may stimulate precocious dehardening.…”

“…If specific pollution events (e.g., high acidic deposition inputs) or unusual climatic conditions (winter thaws) further reduce red spruce cold tolerance during some winters, as laboratory and field experiments have demonstrated (Fowler et al, 1989;DeHayes et al, 1991;DeHayes, 1992;Vann et al, 1992;Strimbeck et al, 6. Causes of Freezing Injury in Red Spruce 189 1995; Schaberg et al, 1996), the frequency and extent of red spruce freezing injury would be expected to dramatically increase in years such impacts are prevalent.…”