Because of their smaller leaf size, several arid-climate plants can preserve water. Water loss via the epidermis is minimized when the leaf surface area is lowered. Smaller leaves have fewer stomata than bigger leaves, which lowers water loss. Some desert plants, such as cacti and succulents, have evolved ways to conserve water by reducing their water requirements during periods of drought. These adaptations include having thick skins that prevent water loss through transpiration, reduced growth rates, and changes in gene expression for photosynthesis.
Plants need water to live and grow. But they also need oxygen to breathe. So how does this affect how much water they require? Well, first of all, not all plants need water at the same time. Woody plants, such as trees, require more water at certain stages in their life cycle than others. For example, when a tree is growing its main body mass, called its stem, it requires more water than when it is bearing fruit, since more nutrients are needed for new seeds or fruits. Vegetative parts of the plant require even more water during hot, dry seasons because they are producing more waste products that need to be removed.
Some plants, like rice and wheat, are grown under conditions where they can absorb water from the soil. Other plants, such as cotton, do not tolerate wet feet well so they need to be watered regularly to keep them healthy.
Several adaptations allow plants to reduce transpiration or water loss from their leaves, including having leaves reduced to spines, which reduces the surface area for transpiration, a waxy leaf cuticle, which stops evaporation because it is impermeable to water, and a reduced number of stomata, which reduces the surface area for transpiration. These adaptations help plants conserve water during periods of drought.
Stomata are small pores on the surface of leaves. When many stomata are open at once, they create a large surface for water to escape through if it enters the leaf through the roots. The amount of space between each pair of veins on the underside of the leaf is called "stomatal spacing". This is another way in which plants reduce transpiration- by making sure that there is not too much water lost through their leaves at any one time.
Reduced stomatal density can protect plants from overheating during hot days. If the temperature inside a plant's leaves rises because more radiation reaches them due to closer positioning of the sun, then this would be expected to lead to increased rates of water loss through the stomates. However, this isn't always the case: when the sun is very high in the sky or at midday, its heat is reflected back up into space, so plants don't need to close their stomates to prevent themselves from being cooked from within.
Plants prevent water loss by shutting stomata, creating thick cuticles, or having enough leaf hairs to form a boundary layer. Stomata respond quickly to environmental signals, preventing the plant from losing too much water while still allowing enough carbon dioxide to stimulate photosynthesis. Cuticles can be made of waxes, oils, or proteins and act as a barrier against moisture loss through evaporation.
Leaf hairs are very fine branches that grow on the leaves of plants. They create a barrier between the plant and its environment that prevents water loss through vapor diffusion. If left unaltered, this barrier would be detrimental to the plant's ability to survive since it would cause the leaf to lose water faster than it could be replaced by precipitation or droplets formed during transpiration. However, plants have evolved ways to remove leaf hairs to allow more light into the canopy and reduce energy consumption due to photophobia. Similarly, they will also remove them if they feel like it can help their plant survive in a drought-stricken area.
Stomata and cuticles are only two examples of how plants protect themselves from drying out. There are many other mechanisms used including chloroplasts which use light energy to make sugar which feeds cells until fuel is needed for photosynthesis again, so more leaves mean more time before you need to refuel.