What Adaptations Do Cacti Have for Life in the Desert?

Roots

• Most cacti have a long tap root that anchors them into surrounding soil. The remainder of the root system is shallow and radial in nature, spreading in all directions from the plant to allow for rapid absorption of water when rain occurs. Lateral roots have a protective cork layer to prevent them from losing water. Some species develop rain roots or root hairs as soon as the soil receives moisture. These roots later dry up and disappear.

Thick, Waxy Stems

• Thick, waxy stems and pads act as a retaining layer to prevent water stored inside from escaping through transpiration, the evaporation of moisture from plants. This epidermal layer also allows for swelling and shrinkage. Cortex and pith tissue composes stem interiors, providing a reservoir for food and water. Woody tissue toward the stem exterior help support the plant when it swells with stored water. Some species have accordion-like stems that allow the plant to easily expand then contract when water is depleted

Spines

• Instead of large leaves, cacti have modified leaves called spines that protect the plant from predators and help reduce transpiration. Spines help break up the prevalent, evaporative desert winds that blow across stem and pad surfaces. They come in many shapes, long, short, thin and hooked, with some spines directed downward to direct moisture toward roots. Hairy spines provide shade from the sun, acting as umbrellas and protect stems from becoming bleached.

CAM Photosynthesis

• Cacti depend on chlorophyll in the green outer cortex of their skins to conduct photosynthesis for food production. Crassulacean acid metabolism, more commonly known as CAM photosynthesis, is an adaptive form of food production used by cacti and other plants in arid climates. In this process, cacti stomata open only at night when plants are relatively cool to minimize transpiration and provide for the exchange of oxygen and carbon dioxide. Carbon dioxide taken in at night is converted to an acid, then stored until daytime when the sun comes out and completes the food production process.