Biocrust and Frost Field Note

Biocrust and Frost Field Note

November 23, 2016

Rebecca Durham shares images and descriptions of frost interacting with lichens, moss, and biocrusts.

Frost finds the awn tips of pinnatifid homalothecium moss (Homalothecium aureum).

A dehisced lupine seedpod seeds ice.

Candle snuffer moss remained frost-free (Encalypta vulgaris). Species’ surface features play a role in when and where ice forms. Hydrophobic, or water-repelling, surfaces will freeze at a lower temperature.

I observed no ice on the surface of pelt lichens (Peltigera spp.). Frost collected on the underside of the lichen, and on reproductive structures (below). Collaborators Dr. Tadd Truscott (Utah State University) and Dr. Lea Condon (USGS, Oregon) and I are studying water dynamics in biocrust lichens. Preliminary data from light and electron microscopy suggest the upper surfaces of some pelt lichens repel water.

Pixie cup (Cladonia spp.) is another lichen that repels water. Here its ice-free form contrasts with twisted star moss’ extensive frost accumulation. Hydrophobic lichen surfaces prevent water from blocking carbon dioxide necessary for respiration, and also affect ice accumulation. Lichens have amazing tolerance to cold and ice, and can photosynthesize at temperatures below zero and under snow.

Many lichens exude a whitish substance called pruina, which looks like frost. These mineral crystals, often made of calcium oxalate, grace the lobe tips of frosted lichen (Physconia muscigena, above) and the surface of some pelt lichens (Peltigera sp., below).

Prairiesmoke, another frost tolerant fall-growing species, collects frost on its leaf tips (Geum triflorum).

Twisted star moss seeds frost from its awn tips in (Syntrichia ruralis).

Minute variations in temperature and humidity, surface structure and characteristics, and microscopic impurities in water all affect crystal formation.

frost

Mushroom with frost

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