Water scarcity is fast becoming one of the major limiting factors in world crop production. In many areas, poor agricultural practices have led to increasing desertification and the loss of formerly arable lands. Consequently, those plant species that are well adapted to survival in dry climates are being looked at for an answer to the development of more efficient crops to grow on marginally arable lands.
Plants use several mechanisms to ensure their survival in desert environments. Some involve purely mechanical and physical adaptations, such as the shape of the plant's surface, smaller leaf size, and extensive root systems. Xerophytes and phraetophytes are two kinds of plants that survive in the desert environment through adaptations of their physical structure. Xerophytes, which include cactuses, an adaptation from the rose family, are effective desert plants because they have spines instead of leaves. These spines protect the plant from animals, shade it from the sun, and help it collect moisture. Another adaptation is their shallow but extensive root systems. The roots radiate out from the plant and quickly absorb large quantities of water when it rains.
The mesquite tree is a type of phraetophyte. These plants have tiny leaves that close their pores during the day to avoid water loss and open them at night when they can absorb moisture. All phraetophytes have developed extremely long root systems that draw water from the water table deep underground. Some phraetophytes have developed a double-root system - the typical long and deep root system to collect ground water and a shallow one like the xerophytes to collect surface water.
Some desert plant adaptations are related to chemical mechanisms. For instance, some phraetophytes depend on their unpleasant smell and taste for protection, while many xerophytes have internal gums and mucilages that give them water-retaining properties. Another chemical mechanism is that of the epiticular wax layer. This wax layer acts as an impervious cover to protect the plant. It prevents excessive loss of internal moisture. It also protects the plant from external aggression, which can come from inorganic agents such as gases, or organic agents, which include bacteria and plant pests.
Researchers have proposed that synthetic waxes with similar protective abilities could be prepared based on knowledge of desert plants. If successfully developed, such a compound could be used to greatly increase a plant's ability to maintain health in such adverse situations as inadequate water supply, limited fertilizer availability, attack by pests, and poor storage after harvesting.