Plants in the Desert

1) Saguaro

-The saguaro grows on the northern and southern slopes of the Sonoran Desert.

-It grows in gravel and rocky soils, usually between he heights of 610 to 1068 meters.

-extracts water from its environment every chance it gets

-Its roots are 2.5 centimeters deep in the soil, so it can soak up as much rain and dew before it evaporates. A giant saguaro can soak up to a ton of water during a heavy rain.

-has a spongy inside layer that helps distribute water in the plant. Its outside skin is pleated, so

when more water is absorbed its outside can expend to make room.

-Growth is very slow (can take thirty years or more before the saguaro can reach 1.5 meters high. After eighty years pass, the plant can be 6 meters tall and still not be full-grown. Two centuries may pass before the plant reaches its mature height)

-By growing slowly, the saguaro expends less energy, food, and water, making it fully adapted to the desert.

2) Living stones (Lithops)

-most of the plant’s leaf surface below the ground

-It is cooler; there is less exposure to drying winds, and less chance of being spotted by a grazing animal.

-Gas exchange occurs underground. The stomata open without any exposure to wind or sun, so water loss is minimized during this process.

-limited amount of leaf surface area exposed to the sun for photosynthesis to supply food for the plant.

-The clear tips of the leaves have a crude optical system that permits light striking the windows to be diffused by crystals of calcium oxalate onto the green photosynthetic area below

-seed capsules will not open to disperse their long-lived seeds until they experience rainfall or heavy dew

3) Joshua Tree

- grows in dry soils on plains, slopes and groves

-small knife like leaves that have a very small surface area

-has a waxy resin that prevents much water from evaporating
-night flying Yucca moth helps pollination

References:

http://www.gatewaytosedona.com/image/articles/1318/Saguaro.jpg

http://faculty.ucc.edu/biology-ombrello/pow/living_stones.htm

http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Lithops-karasmontana-1.jpg/113px-Lithops-karasmontana-1.jpg

http://www.desertusa.com/jtree/jt_o2.jpg

How do desert plants survive?

Desert plants have adapted to the extreme conditions to survive in several ways.

Plants that have adapted by altering their physical structure are called xerophytes (such as cacti, usually have special means of storing and conserving water. They often have few or no leaves, which reduces transpiration.). Phreatophytes are plants that have adapted to arid environments by growing extremely long roots, allowing them to acquire moisture at or near the water table. Perennials are plants that live for several years and annuals are plants that live for only a season.

Plants need to conserve moisture and energy in the dry desert. Many plants slow down growth for half of the year to conserve moisture. Many others also lose their leaves when temperatures become too intense. When the short rain season comes, plants burst into color, sprouting leaves and flowers.

Water conservation is very important for all plants in the desert. Many plants achieve this by losing their leaves in one fashion or another. Some plants shed their leaves during long bouts of dryness. Shedding leaves not only prevents the loss of moisture from evaporation, but also slows the growth of the plant. Slowing growth helps plants use less water, food, and energy during hot seasons.

A large number of desert plants begin as seeds. Seeds can survive without water for indefinite periods of time. Seeds only begin to sprout when the rain washes away anti-sprouting chemicals on their shells. After the rains, the seeds will sprout when the temperatures become more moderate. After these plants sprout they may not live very long, because many desert plants sprout, mature, flower, and then die in a very short period of time.

Other plants have thin, knife-like leaves that prevent water loss by giving the sun a smaller area to evaporate water. Others, like the Joshua tree, have needle-like leaves with a waxy resin that prevents much water from evaporating. Another type of plant, called living stones, exposes only a few of its leaves to the sun. The rest of the plant remains underground, safe from the sun and heat. Other plants remain hydrated with their deep roots. The mesquite tree has roots that can extend 30.5 meters into the ground, tapping water from underground aquifers.

Many plants in the desert are located many feet meters away from one another. One reason may be that moisture is limited so plants must space out. Another concept is that some plants are poisonous to others. Roots of the creosote bush have chemicals on them just for the purpose of keeping other plants out of their way.

One problem to plants living in or near sand dunes was the constant changing and movement of the dunes. When dunes move, it can uproot plants. Thus, grasses and shrubs living in dune areas have developed long, tough roots to hold onto sand dunes.

References:

http://www.trekway.com/united-arab-emirates/images/EAU04_240-desert-survival-guide.jpg

http://library.thinkquest.org/C0113340/text/biomes/biomes.desert.plantadapt.html

The Sahara and its people by Simon Scoones