Elevated atmospheric [CO₂] promotes frost damage in evergreen tree seedlings

Abstract

Growth under elevated [CO 2 ] promoted spring frost damage in field grown seedlings of snow gum (Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO 2 ] (-5·7°C versus -4·3°C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO 2 fertilization and may affect predictions of vegetation change based on increasing temperature. [CO 2 ]; freeze-induced damage; global climate change; ice nucleation; open-top chambers. Key-words: Eucalyptus pauciflora; elevated atmospheric INTRODUCTIONAtmospheric CO 2 concentrations have been increasing since the industrial revolution, and are predicted to reach twice present levels late next century (Boden et al. 1994). It is thought that temperature will increase as [CO 2 ] rises, and that warming may be greater in winter than in summer (Plummer, Lin & Torok 1996). This could lengthen the growing season if evergreen species were able to take advantage of warm conditions earlier in spring when below-ground resources are relatively abundant. However, predictions of plant responses to global climate and atmospheric change are complicated by weather variability (Katz & Brown 1992) and the extent to which elevated [CO 2 ] might affect plant responses to temperature (Long 1991), particularly low temperatures. Some studies have predicted that frost damage may increase for trees that break dormancy too early in spring (Cannell & Smith 1986;Repo, Hänninen & Kellomäki 1996) Here we report the results of a serendipitous experiment. The experiment naturally occurred during a larger fieldbased study aimed at understanding the effects of elevated [CO 2 ] on the interactions between grass and trees during spring. The results were unexpected and showed that one of the most frost-hardy of broadleaved, evergreen species suffered greater frost damage when grown under elevated than ambient [CO 2 ]. MATERIALS AND METHODS Plant material and growth conditionsSeeds of Eucalyptus pauciflora Sieb. ex Spreng. were collected from three trees growing along the floor of the Orroral Valley at an elevation of 850 m in New South Wales, Australia. The seeds were cold stratified under moist conditions at 3°C for 4 weeks before germinating on sand flats in a mist house. Seedlings of similar size were transferred to individual containers (5 cm diameter, 25 cm deep) and grown out of doors for 6 months before the start of the experiment.In a pasture near Bungendore in southeastern Australia (35°15' S, 149°27' E; elevation 700 m), 10 open-top chambers were installed as five replicate pairs, flushed with air containing either ambient or elevated CO 2 conce...

Does Free-Air Carbon Dioxide Enrichment Affect Photochemical Energy Use by Evergreen Trees in Different Seasons? A Chlorophyll Fluorescence Study of Mature Loblolly Pine1

“…Therefore, the slower recovery of F v /F m in plants grown at elevated p CO 2 is indicative of the imposition of an additional stress during the winter, which is not experienced by the control plants. Other evidence that overwintering leaves may be subjected to increased stress at elevated p CO 2 is provided by Lutze et al (1998) who showed increased frost damage to Eucalyptus pauciflora seedling leaves at elevated p CO 2 .…”

The 2007 Eastern US Spring Freeze: Increased Cold Damage in a Warming World?

“…Experimental results suggest that responses are most likely species-specific, but there is a mounting consensus that, for many plant species, growth under elevated CO 2 can reduce their resistance and tolerance to freezing temperatures (Repo et al 1996, Lutze et al 1998, Barker et al 2005, Bertrand et al 2007). The reduction in tolerance appears to be caused by a slowdown in low-temperature acclimation (Loveys et al 2006), which is caused by higher daytime leaf temperatures due to reduced stomatal conductance under ; after the freeze setback, the canopy development resumed but did not achieve the normal level.…”

Impacts of elevated atmospheric CO2 on forest trees and forest ecosystems: knowledge gaps

“…Similarly, the date of bud set in the autumn can either be advanced (Mousseau and Enoch, 1989;Murray et al, 1994) or delayed (Karnosky et al, in press). Both timing of bud break and bud set are important in determining frost and winter hardiness of northern trees species (Repo et al, 1996;Lutze et al, 1998;Wayne et al, 1998). Increased frost injury (Repo et al, 1996;Lutze et al, 1998) and increased winter dieback ) have both been described for trees growing under elevated atmospheric CO 2 in northern regions.…”

“…Both timing of bud break and bud set are important in determining frost and winter hardiness of northern trees species (Repo et al, 1996;Lutze et al, 1998;Wayne et al, 1998). Increased frost injury (Repo et al, 1996;Lutze et al, 1998) and increased winter dieback ) have both been described for trees growing under elevated atmospheric CO 2 in northern regions. Others have described a possible increased cold hardiness for some trees growing under elevated atmospheric CO 2 due to the buildup of soluble sugars that may act as cryoprotectants (Ö gren et al, 1997).…”