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Desert Plants and Threats

Lists and describes various plants of the desert and their adaptations to the desert climate. Lists and expands upon a multitude of threats, caused by both human activity and nature, that affect the desert.

Jordan Said

on 30 October 2012

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Transcript of Desert Plants and Threats

As a result of the little rainfall,
desert plants exhibit several
adaptations that allow them
to conserve water, thus
allowing them to live. PLANT ADAPTATIONS (cc) photo by theaucitron on Flickr Happy desert Since water is necessary for plant life for photosynthesis, which in turn fuels all of their metabolic processes, there is very little plant life in the desert. In the desert, rainfall is rare and falls unevenly during the year. - Plants - The Desert ground Since there is so little rainfall, water easily percolates very deep into the soil, and can stay low in the ground for a long time. Thus, plants have more apical
meristem, cellular regions
where plant growth occurs, in
the roots than the leaves
and stems, as they need
very long roots to access the low groundwater. Phreatophytes - plants that adapt to their
environment by growing especially long roots;
very common in the desert biome. Recall from biology:
Diffusion is the process by which particles move from a region of high concentration to a region of lower concentration. Since the desert climate is so dry and arid, water is always more concentrated, or plentiful, within plants than in the open air around them. On the underside of plant leaves are specialized clusters of cells called stomata. Stomata are holes that a plant uses for gas exchange, releasing oxygen from photosynthesis and absorbing carbon dioxide for photosynthesis. These stomata are controlled by a pair of guard cells, which open and close the hole. When a plant is low on water, the guard cells remain shrunk and keep the stomate closed, locking in remaining water. When a plant has enough water, the guard cells swell and open the stomata--potentially causing the loss of water in a plant! THUS, STOMATA ARE VERY DANGEROUS FOR DESERT PLANTS, BECAUSE A PLANT WILL ALWAYS LOSE WATER WHEN THE STOMATA ARE OPEN! But wait! Desert plants have found a way around this dilemma so that they do not lose all of their water from transpiration. OXYGEN (O2) CARBON DIOXIDE (CO2) STOMATA Guard Cells (2) TRANSPIRATION As you can see, desert plants have little to no leaves. This eliminates stomata from their anatomy, and thus they no longer have any holes to lose water from.

Plants that do retain leaves often have very, very few leaves, which contain little to no stomata on them. xerophytes - plants who conserve water by altering their anatomy to eliminate leaves and stomata, thus preventing transpiration (water loss). For example, let's check out this cactus. It has no leaves! Instead, this cactus has SPINES, which lack stomata and prevent transpiration. Remember, some desert plants do keep their leaves. Instead, their leaves have very few or even no stomata. Desert plants that keep their leaves often have a WAXY CUTICLE LAYER, a thick layer above the epidermis (outermost layer) of the plant that keeps water from leaving through stomata and transpiration. Alternatively, some desert plants may keep their leaves and simply open their stomata for photosynthesis during the night, when temperatures are MUCH cooler and water will less easily escape through transpiration. Let's discuss rainfall again. Rain falls in the desert very inconsistently. Rainfall vacillates between periods of long, dry droughts and extremely short periods of vigorously intense flooding. Plants have learned to response accordingly to the short, intense floods in the desert. Most desert plants, as a result of the rain pattern, are ANNUALS, meaning that only grow once a year. These plants will grow quickly after a flood, germinate, send up shoots and flowers, and die--all within a few weeks of the flood. NOTE: Cactus spines are also especially innovative since cacti can hold large amounts of water inside of their bodies. The spines are a defense mechanism that keep animals from attacking or killing them for their contained water. This is the OPPOSITE of how most plants operate their stomata, opening them during the day and closing them at night. Desert plants reverse this response, and thus their biochemical pathway is specifically called CAM (Crassulacean acid metabolism) Photosynthesis. EXAMPLES Sagebrush (Artemisia tridentata) Creosote bush (Larrea tridentata) (Prosopis velutina) MESQUITE BARREL CACTUS (Ferocactus wislizeni) (Salvia dorrii var. pilosa) DESERT SAGE DESERT STAR (Monoptilon bellidiforme) BRITTLEBUSH (Encelia farinosa) (Echinocereus triglochidiatus) HEDGEHOG/CLARET CUP CACTUS (Yucca baccata) DATIL YUCCA ORGAN PIPE CACTUS (Stenocereus thurberi) THREATS There are four major threats in the desert that cause problems both in the biome itself and exist within the biome that cause problems for humankind. GLOBAL WARMING WILD FIRES IRRIGATION DEVELOPMENT Global warming is the gradual increase in temperatures and climate change in the last few decades as a result of adding excessive amounts of greenhouse gases to the atmosphere. CO2 Global warming is raising Earth's temperature, increasing the chances of severe drought by preventing precipitation (spec. rain) in the desert.

Droughts directly affect the growth of vegetation, which in turn directly affects desert animal life, increasing animal deaths from starvation and dehydration.
As the temperature in deserts increases and watering holes disappear due to global warming, the remaining plant life suffers from a lack of hydration. In these cases, plant life becomes dry and brittle, making wildfires a great danger.
As humans continue to expand into the extreme climates, irrigation systems are set up in deserts. However, there is already so little rainfall that taking rainfall away for irrigation renders plant life impossible. This also disrupts the hydrologic (water) cycle by taking water away from plants and the soil to irrigation pumps, where it cannot cycle nutrients between components of a desert ecosystem. LOS ANGELES, CA LAS VEGAS, NV PHOENIX, AZ Humans have urbanized and spread into the great deserts of Southwest North America. As a result, deserts are shrinking, and irrigation systems are causing plant life destruction. Indicator species are species of animals and plants that indicate nutrient depletion or ecological danger in an ecosystem.

In the desert, there are several indicator species. INDICATOR PLANT SPECIES PRICKLY PEAR YELLOW PALO VERDE SAGUARO CACTUS (Opuntia littoralis) (Carnegiea gigantea) (Cercidium microphyllum) INDICATOR ANIMAL SPECIES (Callisaurus draconides) ZEBRATAIL LIZARD (Procavia capensis) ROCK HYRAX Invasive species are species that adversely affect the habitats and biomes they invade economically, environmentally, and/or ecologically. The main invasive species of the desert is the FOUNTAINGRASS. Fountaingrass is a large grass that produces lots of seeds that spreads rapidly from cultivation into nearby disturbed areas, and eventually into natural habitats. It often forms dense stands and aggressively competes with native species, especially perennial grasses and seasonal annuals, for space, water, and nutrients. (Pennisetum setaceum) (Cactoblastis cactorum) The main invasive species of the desert is the CACTUS MOTH. As a natural feeder on prickly pears, the caterpillars of this moth are capable of destroying plants and populations of these plants. Prickly pear cacti are popular in residential and commercial landscapes throughout the southwest United States and Mexico.
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