Desert plant adaptations

How do plants adapt to living in dry conditions? A reader asked this interesting question a few weeks ago. This article will answer it.

The process by which moisture evaporates from a plant is called transpiration. It as essential to the plant's wellbeing as blood circulation is to an animal. The green parts, particularly the leaves, have numerous small pores which allow the movement of water vapour. Each pore is called a stoma (plural stomata), from the Latin word for mouth, because with two guard cells resembling lips on either side of the opening, it looks like a tiny mouth.

In typical plants, the stomata open during the day when photosynthesis occurs. Carbon dioxide is drawn into the leaf and used to produce sugars. As a by-product, oxygen escapes out the same openings. Along with it, water vapour is released.

As it evaporates, it draws more water up through the stem from the roots, pulling more moisture from the surrounding soil. This process brings important minerals and nutrients into the plant. Long channels of cells called the phloem make up vascular bundles in the stem, which help regulate this flow the same way veins and arteries carry blood through all the parts of our bodies. This aspect of transpiration can be observed in a simple experiment by placing a white flowers such as carnations in water with food colouring.

Sometimes it is said that plants eat with their feet, which are their roots. This isn't actually true, because plants don't eat the way animals do. It's inaccurate to call fertilizer plant food. The main thing plants consume is carbon dioxide, a gas absorbed from the air through the stomata on their leaves. Plants are more factories than consumers, using sunlight to make their own food, the sugars which they shunt around to build and maintain their tissues, and on which animals also ultimately depend for nutrition. The nutrients plants absorb through their roots are more like a vitamin supplement.

A desert presents special conditions to the plants that grow there. They receive a wealth of sunlight, the energy they need to run their factories. But water in the soil is in short supply. In fact plants often receive no water from the soil for months at a time.

Just like we won't starve to death if we don't get a daily vitamin pill, plants can survive without a steady supply of soil nutrients. Water, however, is essential to all chemical processes in living things. So desert plants must hold on to it and keep using it over and over.