Tuesday, February 11, 2014

Surviving the Cold, Part 2: Plants

While living in a temperate climate, when the temperature starts to plunge amazing behavioral changes occur in all forms of life. Winter is often seen as a bare, lifeless landscape... when in reality, life still surrounds us!

This is part two of multi-part series that look into adaptation and coping mechanisms plants and animals use to survive cold weather. Last time we looked at some brilliant survival techniques birds use during the frigid winter months. Today, however, we are focusing on...


Plants... they truly are life-giving organisms. The spring and summer months are full of color. Greens of grasses and trees mix with the vibrant colors of flowers. Not only do they bring us visual joy, but they also provide the oxygen we need to survive.

Plants are natural survivors. All they really need are some nutrients from the soil, water, and sun and they do pretty well OK on their own. In the winter, however, many plants have a rough life. The days are too short to provide them with enough sunlight and the cold air makes growth nearly non-existent. Sometimes the weather gets so cold water freezes. Roots are great tools to absorb liquid water... but ice? Forget about it. These harsh conditions would kill any plant if they didn't have special adaptations for surviving those long, cold, dark winter months.

Many perennial plants, including scrubs and trees, drop their leaves in the winter.
Photo by: Matt Brincka

How cold kills
Before we get into adaptations, we should first figure out how cold weather actually kills plants.

Picture this for me... Imagine if you had to stand outside all winter long, couldn't move, and were completely naked. Think you could last long? I sure couldn't. This is essentially what perennial plants (plants that live more than two years) go through in the colder areas of our globe. Annuals are a whole different picture... which we will cover later.

There are a few ways cold weather can kill a plant. First, the water inside a plant's cells could freeze. Ice takes up more space than water. Ever put a can of soda in your refrigerator for too long and it explodes? That is kind of what happens to a plant's cells when they freeze. Ouch.

Another way cold can kill a plant is when water in intercellular spaces (area outside and between plant cells) freezes. This process actually leads the plant to dehydrate, a similar effect of a plant that is experiencing a drought.

Both of those conditions can kill plants very quickly. Cold-temperatures do have other effects on plants besides the freezing of water. If an extremely warm area, like Florida, experiences unnaturally long periods of cold weather but remains about freezing could see many of their plants start to wilt and die. That is because the cold weather is doing one or both of two things: 1) the fluidity between cell membranes change preventing nutrients from entering and exiting the cells at a normal rate, or 2) the cold weather decreases the enzyme activity in the plant, effectively reducing the metabolism of the plant, meaning the plant isn't receiving the energy it normally needs to survive and, thus, is causing a lot of harm... both of which can lead to the demise of our leafy friends.

On to the adaptations!

Dropping leaves
Believe it or not, but the changing of colors and dropping of leave of deciduous trees and shrubs is a winter weather survival technique! Not to mention they look rather pretty. When a tree drops all its leaves, it does so to prevent water loss from inside the plant.

Most conifers keep their needles year-round, only developing their cones
once warmer weather arrives. Photo by: Matt Brincka

The solution is the solution (cell solute levels)
When we salt our front walk in the winter, the salt dissolves with the ice forming a solution and effectively lowers its freezing point... which means it could be 30 degrees outside but ice won't form on your walkway. Plants essentially do that say thing... but normally with sucrose (sugar) and other organic compounds. By increasing the solute levels in the water found in their cells, plants can actually depress the freezing point of water and stabilize their membranes. The only problem is if it gets too cold that sugar water will ultimately freeze itself.

Some plants are masters at surviving subzero environments. These plants typically develop a type of protein that acts like antifreeze. The proteins are normally excreted by the cells that make them into the cell walls, preventing the freezing of intercellular and extracellular spaces.

Dehydrins are found in a lot of drought tolerant plants, but they are also found to help plants in the cold as well. Dehydrins act as a cryoprotectant, meaning they help protect biological tissues from freezing. Cryoprotectants are very coming is arctic and antarctic insects, fish, and amphibians. Many cold-weather plants (i.e., alpine plants) also have to deal with extreme dryness as well, so the dehydrins help not only with the cold weather, but they make the plant more drought tolerant as well.

Some plants' cells can actually change their cellular membrane lipid (fats, waxes, etc) composition. This alteration allows for the adjustment of fluidity in colder temperatures.

Storage organs
Tree and shrubs are noticeable perennials. The reminder that spring will be here soon. Some perennials are less noticeable because their shoots and leave we know die back every winter. Below ground, it is a different story. Some plants utilize underground storage organs where they store food reserves through the growing season. When spring comes, those reserves are used to grown fresh shoots and leaves. There are a few different storage organs, namely tubers (i.e., potatoes), tap roots (i.e., carrots), and bulbs (i.e., onions). Many trees are also known to send their energy supply (sap) to their roots during the winter for storage until spring comes again.

Not all plants survive the winter months. Plants that live for one growing season or shorter and die when winter comes-a-calling are called annuals. Annuals rely on their progeny (seeds) to carry on their legacy! Seeds are fairly hardy. When planting annuals there is typically a warning to plant the seeds after any danger of frost. That warning typically isn't for the fear of seeds dying, but rather for the fear of seedlings dying! Often annual plants just have to wait for the right conditions for their seeds to sprout, which can be a combination of soil temperature and texture, soil moisture level, and enough light. Sometimes seeds can lay dormant for years before sprouting! Annual plants are shown to distributed in that have predictable habitats with regular cycles. Annual plants that live in unpredictable habitats, such as deserts, have been shown to have seed adaptations with complex dormancy cycles in which they are ready to sprout in a variety of different conditions instead of just the perfect scenario.

Alpine plants have not only developed adaptations for extreme cold, but for
ultraviolet radiation, dryness and an extra short growing season.
Photo by: Matt Brincka

Is that all?
These are just a few common cold weather survival techniques plants use. There are countless studies focusing in on survival techniques of plants in extreme weather. Do be afraid to read up on some of them yourself!

What can we do?
Humans are notorious for bringing non-native plants to their gardens and patios. Many native plants already have the adaptations in place to survive the winter your area naturally experiences. However, if you are worried about your plants... here are a few things to consider.
  1. Bringing your plant pots inside during the winter
  2. Overwintering your fragile and tender bulbs
  3. Take cuttings of specific plants
  4. Winter mulching (an interesting way to keep the ground frozen in the winter... which can be important)

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