Deserts are hot and full of sand, camels, and cacti, right? Not always! In this experiment, you’ll learn how some of the world’s toughest plants survive in cold deserts.
How can a desert be cold? A desert is a place that is arid, or dry, but it’s not always hot. Deserts generally receive less than 50 cm of rainfall every year. Some deserts are both dry and cold, creating particularly challenging conditions for plants. These desert environments often receive most of their precipitation in the form of winter snow. The Gobi Desert in Mongolia is an example of a cold desert.
Life might seem hard enough in these cold, dry conditions, but there’s another complication for cold desert plants: the soil that they live in is very salty. When it does rain in a cold desert, mineral deposits are exposed and get shifted around, mixing salt into the soil.
Xerophytes are plants have many ways of adapting to these dry, cold, and salty climates. One way that xerophytes deal with the dryness is by losing some or all of their leaves when it’s dry or very cold—in other words, they can be partially deciduous. Other plants are halophytes: plants adapted to salty environments. In this experiment, you’ll explore one way that halophytic plants manage their salt levels
- 3 tablespoons salt
- Paper towel
- 2 cups of water
- Large cup
- Small cup
- Fill the large cup with water.
- Fill the smaller cup halfway full with salty water. (Create salty water by putting warm water into the cup and adding three tablespoons of salt. Stir it around until the salt dissolves in the water.)
- Put the two beside each other with at least a cup’s width between them.
- Twist a paper towel into a wick.
- Place one end into the small glass and one into the large glass.
- Take a photo of the towel each day over the course of a week. Record your observations in your notebook. What happens? What does the paper towel look like at the end of the week?
The water travels through the paper towel and forms salt crystals.
In this experiment, you moved salt from place to place through the xylem plant tissues modeled by your paper towel. Xylem tissue in plants moves water up from the roots and into the rest of the plant.
Because some halophytes live in areas like mangrove swamps while others live in dry areas with salty soil, different halophytes manage their salt levels in different ways. Some of these plants have ways of chemically balancing themselves in spite of their heavy salt intake, while others have ways of preventing the intake of salt in the first place. Plants called succulents increase their water content to make the salt less toxic inside their tissues by reducing its concentration. Other plants are actually able to excrete, or remove, salt from their tissues with salt glands (modified stomata) located on the leaves of the plant.
Can you think of other reasons why plants would need to move water from one place to another? Would they need to remove any other toxins from their tissues besides salt? Extend your experiment by placing salt-tolerant and salt intolerant plants into identical pots and spray the soil with salty water. Watch these plants over the course of a week or more. What happens to the plants? Do they look healthy? Can you see any examples of salt excretion?