The cold and blustery winter is upon us. Most of the green plants have dropped their leaves or died back for the winter. The mosses may be the only bit of green that you spot when trudging through the snow on a crisp winter day. Mosses do not die back over winter, instead they hibernate. They go into a state of suspended animation where they can survive freezing temperatures. Exposed to the wind or buried beneath the snow they are quite the winter troopers. Mosses are even able to grow on Antarctica!
How are they able to tolerate freezing temperatures? Well, scientists have been trying to figure this out and they have discovered some of the strategies that the mosses are using.
1) Nagao, M., K. Oku, A. Minami, K. Mizuno, M. Sakurai, K. Arakawa, S. Fujikawa, D. Takezawa. 2006. Accumulation of theanderose in association with development of freezing tolerance in the moss Physcomitrella patens. Phytochemistry 67: 702–709.
In this research article they determined that the mosses load up their cells with a variety of sugars (i.e. sucrose, theanderose) that protect against damage caused by ice crystals. They have to build up these sugars in their cells over time to acquire this freezing tolerance. They can't just jump from the warmth of indoors into the icy cold. If I were to take my mosses from the lab and put them outside they would not survive.
2) Close, T. J. 1996. Dehydrins: Emergence of a biochemical role of a family of plant dehydration proteins. Physiologia Plantarum 97: 795-803.
Dehydrins are a special type of protein that helps the moss cells survive freezing and dehydration, hence the name. These proteins interact with the plasma membrane and other proteins inside the cells. They help to protect them from damage. No matter the amount of protection moss cells do become damaged during freezing, but as long as the damage is not too severe the cells can repair themselves during the spring thaw.
Overall I think that it is a really neat system and I am sure that there is more for the scientists to figure out about freezing tolerance in mosses.
Next time you are out you should shift some snow to check out the mosses beneath, but be sure that you replace the snow that you have moved. The snow can act as insulation keeping the mosses a little warmer and protecting them from the wind. One time when I did dig up a patch and forgot to cover it back up the plants were dead when I returned in the spring. I will not make that mistake again.
The photo to the right is from my annual New Year's Day hike at the James L. Goodwin State Forrest. The only habitat shot that I took was this one of the snowy scenery. We did see a few mosses peaking out of the snow, but it was way too cold for me to take off my gloves to operate my camera more than once. Next time I am out I will definitely take some photos of mosses in the snow. Enjoy the weather!
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