Reduced early growing season freezing resistance in alpine treeline plants under elevated atmospheric CO₂

Abstract

The frequency of freezing events during the early growing season and the vulnerability to freezing of plants in European high-altitude environments could increase under future atmospheric and climate change. We tested early growing season freezing sensitivity in 10 species, from four plant functional types (PFTs) spanning three plant growth forms (PGFs), from a long-term in situ CO 2 enrichment (566 vs. 370 ppm) and 2-year soil warming (1 4 K) experiment at treeline in the Swiss Alps (Stillberg, Davos). By additionally tracking plant phenology, we distinguished indirect phenology-driven CO 2 and warming effects from direct physiology-related effects on freezing sensitivity. The freezing damage threshold (lethal temperature 50) under ambient conditions of the 10 treeline species spanned from À6.7 AE 0.3 1C (Larix decidua) to À9.9 AE 0.6 1C (Vaccinium gaultherioides). PFT, but not PGF, explained a significant amount of this interspecific variation. Long-term exposure to elevated CO 2 led to greater freezing sensitivity in multiple species but did not influence phenology, implying that physiological changes caused by CO 2 enrichment were responsible for the effect. The elevated CO 2 effect on freezing resistance was significant in leaves of Larix, Vaccinium myrtillus, and Gentiana punctata and marginally significant in leaves of Homogyne alpina and Avenella flexuosa. No significant CO 2 effect was found in new shoots of Empetrum hermaphroditum or in leaves of Pinus uncinata, Leontodon helveticus, Melampyrum pratense, and V. gaultherioides. Soil warming led to advanced leaf expansion and reduced freezing resistance in V. myrtillus only, whereas Avenella showed greater freezing resistance when exposed to warming. No effect of soil warming was found in any of the other species. Effects of elevated CO 2 and soil warming on freezing sensitivity were not consistent within PFTs or PGFs, suggesting that any future shifts in plant community composition due to increased damage from freezing events will likely occur at the individual species level.

Effect of Planting Date on Accumulated Temperature and Maize Growth under Mulched Drip Irrigation in a Middle-Latitude Area with Frequent Chilling Injury

“…For the same latitude areas with similar ecological environments, it's potential to obtain high yield when the maize sowing date is in range of 10 days before or after the late spring cold, for a medium-mature variety of maize under mulched drip irrigation. Numerous studies have assumed that chilling injury at each growth stage will lead to varying degrees of yield reduction [13,44,45]. For the early sowing treatments in this study, the late spring cold slowed down maize early growth, but exerted no evident adverse effects on yield benefit.…”

“…Moreover, the decreasing solar radiation and light interception together with low temperature in latter growth stages exerted adverse effect on yield formation for the late sowing maize [18,43]. Numerous studies have assumed that chilling injury at each growth stage will lead to varying degrees of yield reduction [13,44,45]. For the early sowing treatments in this study, the late spring cold slowed down maize early growth, but exerted no evident adverse effects on yield benefit.…”

Changes in alpine plant growth under future climate conditions

“…Thus, if the snow cover is disappearing earlier but frost risk remains constant, which may be expected in a future climate, plants may suffer from freezing damage in early spring frosts (Inouye, 2000). Also elevated CO 2 in the atmosphere and warmer temperatures may change the freezing sensitivity of plants (Martin et al, 2010). Therefore, the view that earlier melt out may only come with the beneficial effects of a prolonged vegetation period may be overly simplistic.…”

Sustainable Land-use Practices in European Mountain Regions under Global Change: an Integrated Research Approach

“…For example, high-altitude soil turf monoliths with their herbaceous vegetation were transplanted from Col du Marchairuz to lower altitudes to investigate the effects of different levels of climate warming and reduced precipitation intensities in interaction with different land-use practices typical for the Jura mountains (Gavazov et al 2013). In Davos, data from a long-term experiment at the treeline on Stillberg were analyzed (Martin et al 2010). In the case study region Valais, field studies and drought experiments investigated the germination, growth, and mortality of different tree species (Brunner et al 2009, Eilmann et al 2009, Dobbertin et al 2010, Eilmann and Rigling 2012, Rigling et al 2013).…”