Soils in Winter

Patricia Hanbidge

December 2, 2024

Key points from this story:

• Soil protects life from winter freezing
• Microbes survive in microscopic water films
• Frogs develop natural antifreeze abilities
• Roots adapt to extreme cold conditions
• Soil contains more microbes than humans
• Microbes decompose organic matter critically

Like plants - soil is essential to life as we know it. Soil protects the roots of plants, animals and microbes from freezing to death in the winter months. As the air above the soil cools to zero degrees Celsius, water that is contained in the topmost levels in the soils will also freeze. This is commonly known as the frost layer and sometimes that layer can be several feet deep, depending on many factors which influence this layer. If we get an early snowfall, it serves as a blanket that will insulate the soil. Soils rich in organic matter will help to hold the heat in the ground during the growing season and an organic mulch on the soil surface will also act as an insulated layer.

But interestingly enough below this frost layer there is a lot of action happening. Some animals will burrow beneath the frost layer in the soil and either hibernate or exist on stored food soils but some of the soil animals have evolved to withstand temperatures below freezing. At least five species of frogs in North America make their own natural antifreeze which allows them to become completely frozen for long periods of time without suffering serious damage to their cells. Many of the soil microbes (bacteria and fungi) are active in winter months. Studies done in Antarctica, show microbial life in permanently frozen ground or permafrost. This permafrost layer is a thick subsurface soil layer that never thaws. It is dry and in my opinion looks and feels like freeze dried food products.

Many of our plants that are perennial in nature and grow in cold climates are also able to withstand extremely cold temperatures due to evolving factors. Some will develop root systems below the frost layer while others will also develop an antifreeze-like situation. The roots will release a lot of water into the surrounding soil and within the cells themselves a higher concentration of sugars and salts will lower the freezing point of the water that is still within and between the cells.

Other tiny organisms within the soil are able to survive by living in a microscopic film of water that adheres to soil particles. The bond energy between the water molecules and soil particles is so great that the thin layer of water does not freeze even at extremely low temperatures. The microbes living within this unfrozen water are able to survive and continue to work consuming organic matter and exhaling carbon dioxide. It is important at this point to think about the fact that a handful of soil contains more microbes than there are humans on earth! Being confronted with facts that are incomprehensible we are getting into the real science of soil!

Microbes, like bacteria and fungi, depend on soil for their homes and their work is to decompose organic matter as well as weather rocks and minerals which provides nutrients within the soil in a form that plants can use. Fungi recycle chemical elements that would otherwise remain locked up in dead plants and animals. Some decompose plant debris as they utilize the carbon and energy that come from the breakdown of dead and decaying plants. Bacteria perform a wide range of chemical transformations which are critical to growing and maintaining a healthy food supply. These millions of different microbes that live in the soil create a biodiversity that is in the most part beneficial to human health. It is our job to ensure that we do our part to keep our soils healthy!