When it’s hot outside, people drink more water to make up for all the water they sweat out through perspiration. So what do plants do to make up for the water lost through transpiration? Plants need water to survive, and hot desert plants are super savvy at keeping water inside them.
In this experiment, you’ll observe desert plant adaptations by working with two different plants: a cactus and a plant with leaves. What happens when they are placed in a hot room?
- One small cactus
- One small leafy plant
- Dry potting soil
- Two small pots
- Spray bottle
- Two plastic bags
- Duct tape
- Kitchen scale
- First, create your pots. Choose two pots that are the same size and fill them with dry potting soil, leaving a small hole where your plant will go.
- Place one plant in each pot.
- Use the spray bottle to spray the soil until it is damp to the touch.
- Put a plastic bag around the base of each pot, and secure it with duct tape to ensure that no water will come out of the pot.
- Now, weigh each pot.
- Put your plants in a warm, dry place. They should be close together so that they experience the same environmental conditions.
- Weigh your plants daily, and track the results on a bar graph. At the bottom you will have the days of the week, and on the side you will show the weight of the plant, including the pot. Do this for at least one week.
- No water can evaporate from the pot, since you’ve covered it with a bag. The only water that can get out is from transpiration, the process of water loss through the plant’s stomata, tiny holes on the surface of a plant that release water and gas.
- Did the plants lose water through transpiration? Compare the weight of each plant at the beginning and at the end of your experiment. Divide each plant’s end weight by its initial (starting) weight to get a ratio. Did each plant lose water equally? How do you think you can explain your findings?
The container with the leafy green plant will lose more moisture than the container with the cactus.
In your experiment, you discovered that cacti are experts at keeping water inside them. Their wavy coating and minimal leaves are both adaptations to hot desert life.
Deserts are ecosystems that get very little rainfall. They can be hot or cold. Since plants and animals need water to survive, deserts are very challenging environments to live in. Hot deserts are particularly difficult places to live in, since they are so warm and dry.
Desert plants have a number of adaptations that help them survive in this challenging environment. Instead of the broad, lush leaves that you find on rainforest plants, desert plants have fewer, wavy leaves. This waxy leaf coating makes it harder for water inside the plant to move to the outside.
Plants use photosynthesis to make their food, a process requiring carbon dioxide and water. Plants get water from the soil, but they also exchange carbon dioxide and water with their environment through stomata. Desert plants have smaller stomata, and they often open these only in the evening, when it’s cooler. This means the plant is better able to control the amount of water that transpires.
Some desert plants take things a step further: they’re drought-deciduous, which means when the going gets hot and dry, they drop their leaves in response. This happens to some plants in the Sonoran Desert, the large desert area in the southwestern United States.
Rain does occur in deserts, and when it does, it often comes in the form of a downpour, where a lot of rain hits the ground at once. This allows seeds to germinate. Some dormant seeds of ephemeral desert plants wait for hundreds of years to have the chance to grow! An ephemeral plant only grows briefly in response to an event like a rainfall. After that, these plants flower and produce seeds, which wait underground for the next downpour. Because individual plants live for only one year, they’re known as annuals.
Desert perennials (plants that live for many years) have a different strategy. The roots of these plants can live under the soil for thousands of years, growing and dying back to match the seasons of rain and drought. This strategy works pretty well, as certain desert perennials are among the oldest plants in the world.
Can you think of other adaptations that would work well for plants in a desert environment? Do some research and see if your invented adaptations actually exist in nature!