Scientists have determined fungus is responsible for the mysterious hair-like ice that can sometimes be found growing on the rotten branches of trees.
This "hair-ice" is usually found on humid winter nights, and researchers are finally getting to the bottom of what causes it to grow, the European Geosciences Union reported.
"When we saw hair ice for the first time on a forest walk, we were surprised by its beauty," said Christian Mätzler from the Institute of Applied Physics at the University of Bern in Switzerland. "Sparked by curiosity, we started investigating this phenomenon, at first using simple tests, such as letting hair ice melt in our hands until it melted completely."
The recent study confirmed a 100-year-old hypothesis made by scientists Alfred Wegene. In 1918, he noticed the hair ice on a wood containing fungus mycelium, which are the threads from which mushrooms grow. The researchers believed there was a connection between the ice and fungus growing in the wood. About 90 years later, Gerhart Wagner, a retired Swiss professor discovered if he treated the wood with fungicide it suppressed the growth of the unusual ice. In this recent study, researchers looked at the different fungi in affected wood samples collected during the winters of 2012, 2013 and 2014 in forests near Brachbach in western Germany, and also looked at the physics of hair ice on samples he collected in a forest at Moosseedorf, Switzerland.
The team determined that liquid water near the branch froze, creating a an "ice front" and trapping water between the film between this ice and the wood pores. Suction created by repelling intermolecular forces pushes water into the wood pores, where it freezes and gradually adds onto the existing ice. The growth of the ice is therefore determined by the wood rays at their mouth.
"The same amount of ice is produced on wood with or without fungal activity, but without this activity the ice forms a crust-like structure. The action of the fungus is to enable the ice to form thin hairs - with a diameter of about 0.01 mm - and to keep this shape over many hours at temperatures close to 0°C. Our hypothesis includes that the hairs are [stabilized] by a [recrystallization] inhibitor that is provided by the fungus," Mätzler said.
The team also found signs of the complex organic compounds lignin and tannin, which are metabolic products of the fungal activity.
These components may be the ones preventing the formation of large ice crystals at the wood surface," said chemist Diana Hofmann.
The findings were published in a recent edition of the journal Biogeosciences.
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