Abstract
Ice nucleation has previously been described in only a few lichens from a single location. Here we greatly extend this work and suggest that in lichens ice nucleation is a water harvesting adaption. Fifty-seven lichen samples from a variety of widespread locations were tested for ice nucleation by differential scanning calorimetry (DSC). Samples initiated freezing in the range -5.1° to -20°C and the median freezing temperature was -7.2°C. The vapour pressure difference between ice and water is significant at this temperature, and so ice grows at the expense of water (Bergeron—Findeisen process). Therefore, the ability to form ice at these temperatures provides a useful water-harvesting mechanism for lichens. Ice nucleation appears to be ubiquitous in lichens and is more likely to be associated with the mycobiont and may influence atmospheric processes.
Highlights
BioOne Complete is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses
All contained ice nuclei, freezing water at temperatures 18–33°C higher than would occur with homogenous freezing (–38°C). This extends the range of lichens tested and suggests that ice nucleation is ubiquitous in lichen
Biological ice nucleation has been mainly studied in bacteria (Morris and Sands 2012), there is an increasing awareness of the relevance to atmospheric process of all biogenic ice nuclei active at temperatures warmer than about –15°C (Després et al 2012 for a comprehensive tabulation)
Summary
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Complete website, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/terms-of-use. When water freezes above –38°C this is termed heterogeneous freezing and is reliant upon the presence of ice nucleating particles in the water These catalyse the phase transition at much higher temperatures by aiding the alignment of water molecules to form the ice embryo (Kajava and Lindow 1993, Vali 1996).
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