Fungus: Exidiopsis Effusa Responsible For Peculiar Hair Ice Mystery

First Posted: Jul 22, 2015 01:40 PM EDT

Chances are, you've probably never seen or heard of hair ice-a white, candy-like floss that adorns the rotten branches of certain trees in humid winters. Researchers were quite puzzled by the crystallized fine, silky ice that makes up this rather peculiar piece of nature. Yet now, a team of scientists from Germany and Switzerland have identified the missing ingredient that holds hair ice in place: the fungus Exidiopsis effusa. The findings are published in the journal Biogeosciences.

Since the initial discovery of this whitish cobwebby coating by Alfred Wegener in 1918, the fungus species and mechanism that drives the growth of the hair ice had yet to be discovered. Yet scientists wanted to know more.

In the latest study, German and Swedish researchers were inspired by photos of hair ice sent from various countries to perform a set of experiments that helped them figure out just what conditions are needed to grow this type of ice and the properties surrounding the growth.

They studied samples of hair-ice-bearing wood collected in the winters of 2012, 2013 and 2014 in forests near Brachbach in western Germany, analyzing the wood samples via the help of microscopic techniques. From there, study results revealed 11 different types of hair ice.

They also performed experiments designed to understand the physics of hair ice. Researchers studied collected samples of hair ice in a forest at Moosseedorf, Switzerland, confirming that ice segregation is responsible for producing the hair ice filaments at wood surfaces. Then, when cold air comes in contact with the water, it freezes, resulting in an ice front that ‘sandwiches' a thin water film between both the ice and wood pores. Additional suction also results as intermolecular forces get the water inside the wood pores to move towards the ice front, where it freezes and adds to existing ice.

Lastly, a chemical analysis of the hair ice, itself, revealed that it contained tiny fragments of the complex organic compounds lignin and tannin. These metabolic products of the fungal activity reveal biological influence on hair ice.

Researchers noted how this somewhat rare and fleeting phenomenon may have taken so long to figure out.

"Hair ice grows mostly during the night and melts again when the sun rises. It's invisible in the snow and inconspicuous in hoarfrost," noted study author Gisela Preuß, a German biologist. He added that hair ice is mainly found in broadleaf forests at latitudes between 45 and 55°N.

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