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Time to chill: effects of simulated global change on leaf ice nucleation temperatures of subarctic vegetation¹

²Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK; ³Centre for Arctic Ecology, University of Sheffield, Sheffield S10 2BR, UK; ⁴Abisko Scientific Research Station, Abisko SE98107, Sweden; and ⁵Institute of Biological Sciences, University of Wales, Aberystwyth, Ceredigion, Wales, 5Y23 5DE, UK

We investigated the effects of long-term (7-yr) in situ CO₂ enrichment (600 µmol/mol) and increased exposure to UV-B radiation, the latter an important component of global change at high latitudes, on the ice nucleation temperatures of leaves of several evergreen and deciduous woody ericaceous shrubs in the subarctic (68° N). Three (Vaccinium uliginosum, V. vitis-idaea, and Empetrum hermaphroditum) of the four species of shrubs studied showed significantly higher ice nucleation temperatures throughout the 1999 growing season in response to CO₂ enrichment and increased exposure to UV-B radiation relative to the controls. The same species also showed a strong interactive effect when both treatments were applied together. In all cases, leaves cooled to below their ice nucleation temperatures failed to survive the damage resulting from intracellular ice formation. Our results strongly suggest that future global change on a decadal time scale (atmospheric CO₂ increases and polar stratospheric O₃ destruction) will lead to increased foliage damage of subarctic vegetation by severe late spring or early autumnal frosting events. Indeed, in support of our experimental findings, there is now some evidence that increases in atmospheric CO₂ concentration over the past three to four decades may already have acted in this manner on high-elevation arboreal plants in the Swedish Scandes. The implications for vegetation modeling in a future "greenhouse" world and palaeoclimate estimates from high-latitude plant fossils dating to the high-CO₂ environment of the Mesozoic are discussed.

Key Words: elevated CO₂ • elevated UV-B • frost damage • global environmental change • ice nucleation temperatures • subarctic

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