- Hanin Al-geizi
Plants require four simple things to live; water, warm temperature, light, minerals and most places that consist partly of these vital requirements, will be hospitable environments for plants. The most important environmental factors to which plants must adapt are water availability, temperature change, sunlight, soil conditions and predation. For any plant to thrive and survive, each of these factors is vital, and plants that have adapted to extreme environments have undergone changes to acclimate and survive. Adaptations happen over time as a response to changing environments. Acclimations allow plants to reduce competition for space, nutrients, predation and increase reproduction. There are some factors which limit these changes: availability of water, light, predation and temperature.
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Land plants have a different set of adaptations as compared to desert plants. Desert plants have adapted to the high temperatures and dryness by changing physically and modifying behavioral mechanisms. When land plants adapted to life on land, they had to face environmental challenges. The plants were used to a water environment and on land they were faced with drying out in the air; whereas desert plants have adjusted to the scarcity of water, land plants developed structural support to protect water, store nutrients and reproduce. Life on land for plants had some advantages: sunlight was abundant, water acts as a filter, altering the quality of light absorbed by the photosynthetic chlorophyll, carbon dioxide is more quickly available in air than water since it diffuses faster in air, land plants evolved before land animals; therefore, until dry land was also found by animals, no predators threatened plant life. These circumstances changed as animals appeared from the water and started feeding on the nutrients in the plants. In turn, plants developed strategies to deter predation: from spines and thorns to toxic chemicals. Early land plants did not thrive far from sources of water and developed survival strategies to fight the dryness, called desiccation tolerance. Many mosses can dry out to a brown and brittle mat, but as soon as rain or a flood makes water available, mosses will absorb it and are restored to their healthy green appearance. Another strategy is to colonize environments where droughts are uncommon, such as rainforests where ferns thrive in damp and cool places. As time went by, plants moved away from moist or aquatic environments and developed resistance to desiccation, rather than tolerance. Plants, such as cacti, reduce the loss of water to such an extent they can survive in extremely dry environments.
Cacti are plants that have adapted by changing their physical structure, called Xerophytes. Cacti have evolved a way of storing and conserving water. They altered their structure in order to resist the high temperatures and scarcity of water. They have fewer or no leaves which minimizes transpiration. Cacti are considered the most drought-resistant plants on the planet due to this adaptation as well as their root systems, and the ability to store water in their stems. Another cacti evolutionary adaptation is that they use spines for shade and have waxy skin to seal in moisture which is also a characteristic of land plants. These spines are a protective measure from animals while shading the plant from the sun and gather water. Extensive shallow root systems are spread in the ground, allowing for them to receive large quantities of water when it rains, they store water in the core of both stems and roots, thus allowing them to survive years of drought on the water collected from a single rainfall.
Phreatophytes are also a type of desert plant that has adapted to arid climates by growing extremely long roots, allowing them to collect moisture at or near the water table. The term phreatophyte means water-loving plant.
Other desert plants that acclimated, have evolved a lifecycle according to the seasons of moisture or cool temperatures. These plants are commonly called perennials meaning they live year after year rather than annuals which only survive a season. Desert perennials thrive by sleeping during dry periods of the year, then springing to life when water becomes available. Most annual desert plants grow only after heavy seasonal rain, then complete their reproductive cycle very quickly. They bloom very large for a few weeks in the spring, accounting for most of the annual wildflower explosions of the deserts. Their heat- and drought resistant seeds remain sleeping in the soil until next year’s rains. Some perennials survive by becoming dormant during dry periods, then springing to life when water becomes available. After rain falls, these plants quickly grow a new suit of leaves to photosynthesize food. Flowers bloom within a few weeks, and when seeds become ripe and fall, they lose their leaves again and re-enter dormancy. This process may occur as many as five times a year. They also have a waxy coating on stems, which serves to seal in moisture during periods of dormancy.
Other desert plants use a combination of many adaptations. Instead of thorns, they rely for protection on a smell and taste wildlife find unpleasant. They have tiny leaves that close their stomata (pores) during the day to avoid water loss and open them at night to absorb moisture.
Desert plants must act quickly when heat, moisture, and light goes inside of them, let’s just say it is time to bloom. Another plant adaptation important to the survival and early dominance of flowering plants is the production of secondary plant metabolites. These bad tasting and sometimes toxic compounds have been one of plants most powerful means of defense. These are the defensive mechanisms, which the desert plants use to check predators.
Desert plants have taken land plant adaptations to an extreme and survive due to these changes. Land plants still thrive but these desert plants will be around even after land plants are unable to acclimate. All in all, without water, sunlight, warm temperatures and nutrients neither type of plant has a chance of survival.
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