How do desert plants survive?

In deserts,the temperature in the day can rise above 45 degrees celcius.As most deserts are  found near the equator the temperature range can be very extreme. As it is very hot, animals are rarely found there and minimal plants survive in the desert.So, how do desert plants survive?

The most essential need for a plants is water,as sunlight ,oxygen and carbon dioxide are abundant.In the desert, there is hardly any rainfall. Even though sunlight is always recieved in the desert,there is no water for evaporation,thus the water cycle cannot occur.Thus, there is only minimal life found in the desert.

Plants use water that has been stored in soil pores.in dry areas plants naturally tend to grow some distance apart,giving each of them a cahnce to tap water from a large area when there is no rain.Plants that grow naturally in areas with a drought have two ways of coping with dry soil.Many plants have long roots that sink deep into the soil and sometimes into the aquifer below. Other plants spread out huge nets of roots through the soil and thus gather moisture from a wide area.Plants can also stop water from evaporating from their leaves(they are deciduous).They have thick waxy leaves with very few pores that reduce the amount of water evaporated during transpiration. Some plants also have thin needle-like leaves that reduce the surface area of the leaf thus reducing the amount of water loss during tranpiration.

Plants also can adapt to dry areas by behaviorial adaptations. Desert plants could also have developed a lifestyle in conformance with the seasons of greatest moisture and/or coolest temperatures.These type of plants are usually (and inaccurately) referred to as perennials, plants that live for several years, and annuals, plants that live for only a season.Desert perennials often remain dormant during the hot and dry periods of the year.When water is available, they would then start growing.Most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.They also have drought -resistant seeds, that would remain dormant until the dry period is over.


Xerophytes are plants that change their physical structure to adapt to the environment to reduce the amount of water loss during tranpiration. Desert xerophytes such as cactus, are among the most drought-resistant plants on the planet due to their absence of leaves, shallow root systems, ability to store water in their stems, spines for shade and waxy skin to seal in moisture.Cactus plants can also photosynthesise using their stem in subsitute of its leaves.Its leaves are spiny .long and narrow to reduce the amount of water loss during transpiration.

Phreatophytes, like the mesquite tree, have adapted to desert conditions by developing extremely long root systems to draw water from deep underground near the water table. The mesquite's roots are considered the longest of any desert plant and have been recorded as long as 80 feet.

The Creosote Bush is one of the most successful of all desert species because it utilizes a combination of many adaptations. Instead of thorns, it relies for protection on a smell and taste wildlife find unpleasant. It has tiny leaves that close their stomata during the day to avoid water loss and open them at night to absorb moisture.
 
Some perennials, such as the Ocotillo, survive by becoming dormant during dry periods, then springing to life when water becomes available. After rain falls, the Ocotillo quickly grows a new suit of leaves to photosynthesize food. Flowers bloom within a few weeks, and when seeds become ripe and fall, the Ocotillo loses its leaves again and re-enters dormancy. This process may occur as many as five times a year. The Ocotillo also has a waxy coating on stems which serves to seal in moisture during periods of dormancy.


Annuals
Contrary to the usual idea that deserts are uniformly hot, dry and homogeneous in their lack of plant life, they are actually biologically diverse. Each season's unique precipitation pattern falls on a huge variety of mini-environments.

Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are the sprinters of the plant world, sending flower stalks jetting out in a few days. The peak of this bloom may last for just days or many weeks, depending on the weather and difference in elevation. 

Links to very interesting videos about desert plants:
http://www.youtube.com/watch?v=UkqfIQ6I-6I
http://www.youtube.com/watch?v=jlaMBqS88EA&feature=related


Plants found in deserts:Joshua tree,Cacti,Palm trees,Yuccas.

Sources: the living world(book);http://www.desertusa.com/du_plantsurv.html