Spiny Desert Plants - Cactuses

Cacti/cactuses nowadays come to mind as plants that collect radiation. And in the past, they were the saviors of film heroes who were thirsty in Western films mostly. First of all, it was not obtained any scientific data yet about the fact that cacti collect radiation rays. For now, we can say that this information is a myth that circulates among people. On the other hand, even knowing how cactuses cope with thirst is enough to be impressed from them.

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Well, then what is the difference between cactuses and other plants? What does the spiny structural feature give them? Where does the cactus's relationship with the desert come from? Can they bloom? Are the cactus species living in the desert really a water reservoir?

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The homelands of the cactuses are America and the periphery islands, and most cactus species are found in Mexico. This plant from the Cactaceae family has 5000 species in nature. We can say that having such diversity is influenced by high adaptability to hot and arid areas mostly.

The ability to survive in the Atacama Desert in northern Chile, known as the world's most arid desert (annual rainfall of 200-500 mm), shows how successful their adaptation to arid life is. Before describing the superiority of cacti over other plant families, let me briefly mention photosynthesis.

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Jan Baptista Van Helmont, a physicist who lived in the 17th century, is known as the first researcher on plant material synthesis. The researcher planted a willow seedling weighing 2.5 kg in a pot with 100 kg of soil and watered it for 5 years with rainwater only. At the end of the period, the seedling was a tree of 85 kg. At the end of the trial, the dry soil weight was determined as 99,994 kg. The difference of a few grams was regarded as an experimental error, and it concluded that the increase of 82.5 kg of substance in plant weight was caused by water only. Van Helmont's attempt to discover is that plants produce own food under sunlight, that is, photosynthesis.

When plants produce the food, they do not only benefit from the soil. In addition to minerals in the ground, they use water and CO₂ in the air to produce the foods they need in daylight. The leaves enter the circuit at this stage. There are small holes called "stoma" that allow gas exchange on the leaves and body of plants.

Water from the soil, CO₂ from the air, and sunlight are converted into starch and other high-energy carbohydrates by photosynthesis reactions. The oxygen resulting from this reaction is released into the air. The plant then uses the energy it stores in these carbohydrates when it needs food. In the meantime, with the opening of the pores, the water in the leaf evaporates and leaves into the air. With the help of the pressure difference created by the lost water, the plant recovers its water from its roots. This process can be expressed as follows.

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nCO₂ + 2nH₂O + Light Energy -> (CH₂O) n + nO₂ + nH₂O

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However, because thick and droughty plants like cactus live in warm and dry environments, photosynthesis (like the ones above) will cause them to die. Because when they receive CO₂ they will have to give in their water and they will dry out because their water reserves will be exhausted.

For this reason, cactuses developed a different breathing technique than other plants. With this system called Crassulacean Acid Metabolism (CAM) photosynthesis, CO₂, unlike other plants, is taken away from the air at night and stored while keeping the pores open. In the daytime, the pores are closed to prevent sweating and therefore water loss. But, photosynthesis continues through stored CO₂. The only disadvantage is that the growth rate of the plant is low because the photosynthesis did in this way normally provides less energy. Some species perform normal photosynthesis in abundant water, then use CAM photosynthesis. This respiration method, which is seen in arid plants like cactus, allows them to live in arid regions. In this way, it has specified that the cactuses were sweated by about 1 in 30 in the normal tree leaves. Thorn-shaped leaves reduce the surface area to a minimum and so sweating is kept to the minimum.

Cactuses rescue people and other living things facing the danger of dying from thirst in the desert thanks to their designs in the structure. For example, we can say that the regions where the giant cactuses located in the Arizona Desert are real oases. These giant cactuses, like a water station, provide water needs of all living creatures, especially birds in the desert. The cactus, called Saguaro, is one of the largest cacti in this sense. Adults usually reach 12 meters in length, rarely more than 15 meters.

Many of the cacti, like flowering plants, bloom and grow regularly every year if they are cared for. The cactus, which does not get water for a long time, will go to sleep after a while. This will mean that if it is not the right time it will stop the growth of the plant. Under normal conditions, cacti spend a considerable part of their winter and summer seasons and spring months asleep. In this phase, water brings about 75% of the weight of the cactus to the pitch and loses about 70% of its weight during the dry season. To overcome the problem of drought, they have established a short life cycle. Thus, together with the beginning of the rains, they flourish quickly, and one month later they begin to produce seeds.

Besides all these beauties, some cactus species are used as both food and medicine source. It is utilized from the fruit of the Opuntia species, in particular, the fruit and oil of the Oftcus-Indica. Some cactus species with mescaline (intestinal softener), such as Peyote, have also been used as medicines since ancient times.

Because cacti do not want much water, the best kind of planting is at home. You can turn a corner of your home into a cactus garden by fertilizing once a year and changing the pot every 5-6 years.

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Image Sources

• Tall cactuses in a desert
• Red Rock Cactus - Arizona
• Diagram of the photosynthetic process
• A simplified view of the CAM

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Sources

• John King, Reaching for The Sun, 1997, Cambridge University Press, Cambridge, s.18
• https://en.wikipedia.org/wiki/Cactus
• http://onlinelibrary.wiley.com/doi/10.1111/nph.13127/full