There are many hot and dry parts of the world where rainy days are rare and it can take months for a few drops to fall. The absence of rainfall causes a dry climate but if it is also accompanied by long days of sun and heat, the drought worsens, which affects the vast majority of plants.
The drought causes the dehydration of the plants because they lose water when they perspire that they cannot recover because their roots do not absorb enough. Dehydration can be seen through the leaves, which turn yellow to wilt. The same happens with the shoots and with the plant in general, which looks fallen and lifeless. If the situation worsens, the plant dies.
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The adaptation of the leaves
Now there are some plants that have developed different mechanisms to withstand drought and thus defend against this situation. And we don't talk about succulent plants, which have the power to store water in their thick bodies in order to tolerate the days without water. There are drought resistant plants that have developed other types of mechanisms that help them survive until the rains appear.
This is the case of oleander which, like other species, have adapted its leaves. Thus, there are plants that have developed small but thick and hard leaves, with special stomata that are located on the underside of the leaf and are protected from the sun. This morphology limits the loss of water that occurs through evaporation. They are very special evergreens that help plants survive. Plants with these adapted leaves are called sclerophyllous plants, as with the strawberry tree, holm oak and other species.
In other cases, what we appreciate is another mechanism to prevent the plant from perspiring excessively and thus losing the least amount of water possible. There are xerophilic plants what are they presenting leaves with little surface area exposed to the sun. Instead of the leaves being spread out, they grow curled, linear, narrow, or needle-shaped so that evaporation is minimal. This in turn has consequences because, because the leaves are smaller, the photosynthesis process is slower and, therefore, the growth of the plants as well.
Our drought resistant plants they can also present hairy leaves that ensure less water evaporation. When covered by a layer of white hairs, they reflect light and thus decrease in heat on the surface of the leaf, leading to less evaporation. In turn, the pilose surface helps to capture moisture from the air. An example to discover? Sage
One step further is that of cacti, which manage to survive avoiding the presence of leaves. These plants have adapted to the conditions in which they live by developing thorns instead of leaves to reduce perspiration and, consequently, the loss of water that always occurs through the leaves.
Double root system
Finally, we have those drought resistant plants that instead of transforming their leaves have developed a double root system, a very deep one, in order to extract water from the deepest layers of the soil. These plants first develop the deepest root system and then the most superficial, which uses the water from the little rainfall it receives. Once their double root system is formed, these plants begin to develop the aerial part, but the process can take years. The Cistus salviifolius, better known as Rockrose, is a plant with these characteristics.
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