Other succulent plants, like the agave (above), store water in their fleshy leaves, stems, or roots.
Desert plants may have a completely different appearance from regional native plants. They frequently have inflated, spiky, and small, rarely bright green, leaves. Their impressive adjustments to the difficulties of the desert climate are the cause of their peculiar look. The only characteristic that distinguishes a desert and the main constraint to which desert species must adapt is aridity.
Succulence, drought tolerance, and drought avoidance are the three main adaptive mechanisms that desert plants have developed. These are all distinct but useful sets of adaptations for thriving in environments where plants from other places would perish.
Succulence
In their soft leaves, stems, or roots, succulent plants store water. All cacti, as well as non-cactus desert residents including agave, aloe, elephant trees, and numerous euphorbias, are succulents. The water storing habit cannot function without a number of additional adjustments.
After focusing all of their energy on developing seeds, drought-resistant plants such as California poppies and owl’s clover eventually perish.
A succulent needs to have the capacity to absorb a lot of water quickly.
Desert rainfall are frequently modest and fleeting, and the hot sun causes the soil to dry out quickly. Nearly all succulents have vast, shallow root systems to adapt to these environments. Saguaro plants have roots that reach horizontally nearly as far as their height, but they are rarely deeper than four inches (10 cm). The majority of the water-absorbing roots are in the top half inch (1.3 cm).
Succulents need to be able to use their water reserves as well as possible in a drying climate. Most species’ stems and leaves have waxy cuticles that, when the stomates are closed, make them practically impermeable. Reduced surface areas further conserve water; most succulents have few leaves (agaves), none (most cacti), or deciduous leaves during dry seasons (elephant trees, ocotillos, boojums).
A water-efficient form of photosynthesis known as CAM, or Crassulacean Acid Metabolism, is found in many succulents as well as semisucculent plants like most yuccas, epiphytic orchids, and xerophytic bromeliads. CAM plants store carbon dioxide and open their stomates for gas exchange at night. The stored carbon dioxide is used for photosynthesis during the day, when the stomates are closed. In comparison to conventional C3 plants, CAM plants lose one-tenth as much water per unit of carbohydrate produced at night because of the lower temperatures and higher humidity.
The ability of CAM plants to maintain an idle metabolism during droughts is another advantageous quality. Stomates in CAM plants remain closed day and night when they are under water stress, which virtually stops gas exchange and water loss. However, the plant keeps its metabolism at a low level in the moist tissues. An idle CAM plant can restart full growth 24 to 48 hours after a rain, just like an engine can accelerate to full speed more quickly than one that is cold. Succulents can so quickly benefit from transient surface wetness.
In a dry area, stored water needs to be protected against creatures who are thirsty. Most succulent plants are poisonous or prickly, and frequently both. Some species defend themselves by only growing in remote areas. Others utilize concealment. For instance, the dry stems of the plants it grows in closely resemble the Arizona night blooming cereus.
Drought Tolerance
A plant’s capacity to survive desiccation without perishing is referred to as drought tolerance (or drought dormancy). During dry spells, plants in this group frequently lose their leaves and go into a profound slumber. Dropping leaves conserves water in the stems since transpiration through leaf surfaces accounts for the majority of water loss. Some plants with resinous coatings that prevent water loss do not typically lose their leaves (e.g., creosote bush).
Compared to plants in wetter regions, drought tolerant shrubs and trees have broad roots that can extend up to twice as wide as the canopy. They penetrate the soil more deeply than the roots of succulents, and occasionally they reach extremely deep levels (e.g., mesquite). However, the majority of a mesquite’s roots are found three feet (0.9 m) or less below the ground.
Growth cycle opportunities are controlled by rooting depth. Contrary to succulents’ shallow-rooted technique, shrubs and trees need a significant amount of rain to saturate their deeper root zones. It takes a few weeks for plants like brittlebush and creosote to emerge from deep slumber after a heavy rain. The disadvantage of this method compared to that of succulents is that, after receiving multiple showers, the deeper soil retains moisture for a considerably longer period of time than the upper layer, allowing for several weeks of growth.
Only when the earth is almost completely saturated can succulents absorb water. Conversely, drought-tolerant plants may take up water from considerably drier soil. The low leaf moisture contents that these plants can photosynthesize with would be lethal to most plants.
Plants that can withstand drought, like this brittlebush, frequently lose their leaves and go into deep dormancy when the weather is dry.
Drought Avoidance
By not existing, annual plants avoid harsh circumstances. They grow to maturity in a single season and then perish after using all of their life force to produce seeds rather than saving any for future survival.
The majority of Sonoran Desert annuals only have a brief window in the fall, after summer heat has subsided and before the onset of winter cold. For the majority of species, there must be a drenching rain of at least one inch during this window of opportunity. An inch of rain in the mild fall weather will give enough soil moisture to ensure that seeds will likely grow and produce seeds even if nearly no further rain falls during that season. This combination of conditions is survival insurance. There is still further protection because not all seeds will germinate, even in ideal circumstances; some will remain dormant. A portion of the desert lupine seeds produced each year do not germinate until they are 10 years old, yet the mechanisms underlying this phenomenon are unknown.
During the pleasant fall season, seedlings quickly create rosettes of leaves, rest flat against the ground over the winter as they grow more slowly, then bloom in the spring. Many people believe that spring rains are the cause of our wildflower displays because plants are barely noticeable until they start the spring bolt.
Only in communities with dry seasons are annuals prevalent because perennial plants need a certain amount of root space to acquire enough moisture to survive the driest years. A population of quickly developing annuals can take advantage of both open space and moisture in the rarer rainy years. The fraction of annual species increases with habitat aridity. The Sonoran Desert’s vegetation is made up of annual species to a certain extent. Up to 90% of the plants in the driest ecosystems are annuals.
Although the desert may appear hostile, this is only the perspective of an outsider. Native plants and animals are able to thrive here most of the time thanks to adaptations.
How do succulents hold onto their water?
The desert is really warm. It’s also horribly dry. Succulent plants that store a lot of water in their roots, stems, or leaves, like cactus, aloes, and agaves, can withstand the dry heat.
How? First off, succulents quickly absorb a lot of water when it does rain. Water evaporates quickly in the desert, never penetrating the soil deeply. As a result, the majority of succulents have deep but shallow root systems. Just a half inch or so below the surface, their roots begin to absorb water.
Numerous adaptations have been made by succulents to hold onto this water. They frequently have a heavy waxy coating, which aids in keeping moisture in.
Stomates, which are extremely small pores on all plants, allow them to absorb gases for photosynthesis. But water can also escape through these pores. Less water can evaporate through stomates per cubic inch in succulents. Succulents also have a smaller leaf surface area and, if any leaves exist at all, they are thick and meaty.
Additionally, many succulent plants have changed photosynthetic processes. During the day, other plants open their stomates to absorb carbon dioxide for photosynthesis. To take in carbon dioxide, which they store until the next day, many succulents, on the other hand, retain their stomates closed during the heat of the day and open them in the cool of the night.
Finally, due to the scarcity of water in the desert, succulents must defend themselves from hungry animals. In certain circumstances, these plants are poisonous, thrive in inhospitable places, or are camouflaged to protect their water supplies. In other cases, they are spiky like many cactus.
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What explains why succulents hold water in their leaves?
The desert thorn-apple is an annual plant, which means it grows for a brief period of time before producing seeds and dying. The following year, the seeds will grow into a plant. picture by Neelix
Succulents are cacti and other plants that store a lot of water to help them survive the dry seasons. These plants soak up as much water as they can after even mild rains, storing the water in enormous storage regions in the roots, leaves, or plant stems.
Only during the wet season do some plants survive and flourish, and these plants then produce seeds that can survive the dry season. These plants are annuals since they come again every year, therefore the name. As a result, the adult plant, which transpires more water than a seed, stays out of the hot, dry conditions of the dry seasons.
However, during the dry season, some perennial plants, which are plants that exist for several years, may go dormant or inactive.
Sharp spines are used by many cacti to help shade the plant and deter some animals from eating it. Photograph by William Warby.
During the dry season, many desert plants either lose their ability to hold large amounts of water, perish, or go dormant. In contrast, these plants can endure the hottest and driest times of the year.
These plants are able to survive in the desert thanks to a few distinct strategies. The cactus and certain other plants’ pointed spines serve to screen the plant from the sun and keep it cool. Some plants, such as mesquite trees, develop extraordinarily long tap roots that can descend more than 100 feet to obtain groundwater, which is water that is stored deeply underground.
How much water can a succulent store?
Smaller succulents typically require more water than larger ones, as you’ll discover. The primary factor is that larger succulents are better able to store more water.
Every 1-3 weeks, smaller succulents will require more frequent watering. Larger species, however, can survive 1-6 months without watering.