Plants in the Desert

Hypothesis

Background information

Procedure

Materials

Observations

Conclusion

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Background    Information

            In order for plants to survive in the desert they must make adaptations. One of the most important adaptations is to prevent water loss. Any plant that makes adaptations to survive in extreme heat or lack of water is called a Xerophytes. The most common kinds of Xerophytes are cacti and succulents. The three main ways that Xerophytes prevent water loss is reducing transpiration, increasing water storage and growing during early hours and cooler seasons. Cacti are plants that have areoles. Areoles are the base of a spine or spines that is not connected to the plant. Succulent’s spines grow directly out of the succulent layer. Succulents have a special photosynthesis called Crassulacean Acid Metabolism. Survival in the desert requires plants to adapt their most important survival technique to conserve scarce water.

            A desert is any place where evaporation exceeds precipitation. In most deserts their is no more then 10 inches of precipitation per year. There are three major ways that plants get water in the desert. In the spring as the snow melts in surrounding mountains it drains into the desert. Some of this drainage will cause underground rivers deep below the desert surface. There are occasional rain storms the come usually in the spring. These storms are so intense that the desert cannot absorb the rain fast enough. This causes flash floods and fills old river beds. When the atmosphere of the desert cools it may cause some precipitation because of the drop of solubility. Severe lack of water is a plant’s main problem in the desert. There is plenty of sunlight in the deserts because they are close to the equator and clouds are rare. Deserts with soil have excellent soil for plants. There are many nutrients trapped in the soil and pH levels are prime. Sand and rock deserts do not have as many nutrients but let the roots travel quickly because they are so permeable. Plants in the desert must conserve their water and transpire one thousandth that of regular plants.

            Reducing the amount of water that plants loose through transpiration is key to survival in the desert. One way to cut down on transpiration is to have less area exposed. Small, few or no leaves is common in the desert because of their large area and small volume. Leaves are critical to photosynthesis because they have so much exposed to the sun. Some desert plants have leaves but only during the growing season when it is cool and moist. To compensate for fewer leaves the body or stem of the plant contains cells essential for photosynthesis, chlorenchyma and chlorophyll. A thick waxy layer or cuticle acts as a sealer to not let water out. There are very few stomata on desert plants which helps reduce water loss. Many plants have a sort of hair or fur that surrounds the plants so they are protected from the elements, heat and wind. Stomata on desert plants stay closed during the hottest part of the day and open only for a short while at night. This allows the plants to be completely sealed during the hottest part of the day. If the plant is completely sealed this allows it to store water.

            Water storage is essential for desert plants. Some cacti and succulents store water for long periods of time. They do this so they have some source of water during the driest seasons. Water is stored in parenchyma tissue located in the stem or body of the plant. Others plants specifically succulents store water for only half a day or less. Since water is critical to the light reaction of photosynthesis it is needed during daylight hours. There are problems getting water during the day that have already been discussed. Some plants can take in water at night and store it throughout the rest of the day so the plant has water for photosynthesis. Their is another element critical for the light reaction that is not easily obtained during the day.

            Crassulacean Acid Metabolism is special type of photosynthesis that only succulent xerophytes can perform. Carbon Dioxide (CO₂ ) is hard for plants in the desert to take in during the day without loosing water. CO₂ is large molecule and water is a very small one. If stomata were to open during the day water would slip out while CO₂ is coming in. CAM photosynthesis is when plants store CO₂ in them during the night to use during the day. By storing water and carbon dioxide in them they can perform the light reaction sealed off from the heat and dryness.

            Plants can escape the harshest season the same way some mammals do. Many desert annuals complete their life cycle during the cool and moist spring. Once the extreme heat comes the plant goes dormant. Plants also stock up with water before the scorching summer. Almost all the time stomata is open it is early morning or night. If the plants cannot store enough nutrients and water for the dry season they must get water elsewhere.

            The taproot system is common among desert plants. The taproot is a very small long root that travels very deep to find water. Some taproots go as far as three hundred feet deep to find water. These roots are specially made to transport water quickly to the plant. Another may roots help is to trap moisture. The roots become so thick and dense as to trap water just below the surface. This is common in desert grass and shrubbery.

            All these ways of conserving water are the reason plants can live in the desert. Plants of the desert have adapted very well to their surroundings and perhaps are a "smart" plant. The plants have made other adaptations to survive other then water loss prevention, like thorns so they are not eaten. Plants of the desert are amazing because of the way they conserve their scarce water.