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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 21 | Copyright
Atmos. Chem. Phys., 18, 16063-16079, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Nov 2018

Research article | 08 Nov 2018

Birch leaves and branches as a source of ice-nucleating macromolecules

Laura Felgitsch1, Philipp Baloh1, Julia Burkart1, Maximilian Mayr1, Mohammad E. Momken1, Teresa M. Seifried1, Philipp Winkler1, David G. Schmale III2, and Hinrich Grothe1 Laura Felgitsch et al.
  • 1Institute of Materials Chemistry, TU Wien, Vienna, 1060, Austria
  • 2School of Plant and Environmental Sciences, Virginia Tech, 24061-0390 Blacksburg, Virginia, USA

Abstract. Birch pollen are known to release ice-nucleating macromolecules (INM), but little is known about the production and release of INM from other parts of the tree. We examined the ice nucleation activity of samples from 10 different birch trees (Betula spp.). Samples were taken from nine birch trees in Tyrol, Austria, and from one tree in a small urban park in Vienna, Austria. Filtered aqueous extracts of 30 samples of leaves, primary wood (new branch wood, green in colour, photosynthetically active), and secondary wood (older branch wood, brown in colour, with no photosynthetic activity) were analysed in terms of ice nucleation activity using VODCA (Vienna Optical Droplet Crystallization Analyser), a cryo microscope for emulsion samples. All samples contained ice-nucleating particles in the submicron size range. Concentrations of ice nuclei ranged from 6.7×104 to 6.1×109mg−1 sample. Mean freezing temperatures varied between −15.6 and −31.3°C; the range of temperatures where washes of birch pollen and dilutions thereof typically freeze. The freezing behaviour of three concentrations of birch pollen washing water (initial wash, 1:100, and 1:10000) were significantly associated with more than a quarter of our samples, including some of the samples with highest and lowest activity. This indicates a relationship between the INM of wood, leaves, and pollen. Extracts derived from secondary wood showed the highest concentrations of INM and the highest freezing temperatures. Extracts from the leaves exhibited the highest variation in INM and freezing temperatures. Infrared spectra of the extracts and tested birch samples show qualitative similarity, suggesting the chemical components may be broadly similar.

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Short summary
Birch trees are possible sources of ice-nucleating macromolecules (INM). Pollen of birch trees are known to be ice nucleation active and were recently shown to release INM. For our work we examined 30 samples of birch branches, consisting of leaves, secondary wood (brown with no photosynthetic activity), and primary wood (green, photosynthetically active). The samples were milled and extracted aqueously. All samples contained INM. Most samples froze at temperatures comparable to birch pollen.
Birch trees are possible sources of ice-nucleating macromolecules (INM). Pollen of birch trees...