This is a very good question. When Dr. Alex L. Shigo died, he had been working on research about roots under the ice under the water in ponds and his swamp. Somewhat along the lines of your question. Here he writes about some of it.
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"Frozen cavities in soil. Mycorrhizae layer cavities frozen. Water in soil cavities rarely freezes because the snow on top acts as a very good insulator. When there is little or no snow, all the small amounts of water in cavities does freeze. When cavities has very little water due to low amounts of rain, the situation becomes much worse. The reason is that the mycorrhizae in the cold soil depend on water to do their work. When there is no free water, the mycorrhizae do not work. Deficiency problems usually happen the next growing season. The situation was discussed by Dr. Rene Pomerleau many years ago. Soil does not freeze, but water in cavities does freeze."
"A name is needed for the organs, as synergetic associations, with trees and other organisms, under snow, ice, and water".
"Should the organisms associated with the roots be more correctly termed oomycetes than fungi? Very few people look for mycorrhizae in winter, and further, under water covered by ice and snow. Trees may be dormant above ground in winter, but not dormant below ground." "Cold and ice can stimulate life, or destroy it. Ice and cold can kill plants and animals. Above ground ice can kill as twigs, and stems, fracture. Below ground ice expands soil to for cavities that support life. Cold water can hold more oxygen than warm water. Fish know this! Warm climates support an abundance of life. Many organisms know this. Hydrogen dioxide as solid ice, liquid water, and vapor as a gas, is in many ways, the essence of life."
"As ice forms and thaws in soil, minute cavities form that support the growth of many types of microorganisms, insects, and other life forms. These cavities are not the same as those formed by fracturing tools that make enormous holes in soil. Even smaller cavities result when fungus hyphae die. The minute cavities allow air and water to get into the soil. Compaction is the major disrupters of cavities. This is why mulch of decomposed plant parts is so essential for soils. In climates that have cold winters, ice in soil is essential for the health of organisms in the soil as well as organisms such as plants growing in the soil but getting food from the sun. When the ice does not form, there may be problems for plants."
"Cells die when ice crystals form in the walls and spaces between cells because water in the cells flows outward. The cells die from dehydration. Water flows outward because the concentration of liquid water decreases as ice forms and a concentration gradient forms; flow of liquid water goes from high concentration to low concentration due to the ice crystals that reduce the amount of liquid water."
There is alot more where this came from. If I can help you regarding this type of information please email me.