Few things in nature invoke such a positive response in humans, as the scent of freshly cut grass. The crisp, green smell released by the plants is associated with the warm, carefree days of summer and tends to remind us of our youth, when life was not so complicated. However, according to scientists there may be much more behind it than just a simple odor.
Unlike most animals, whenever threatened plants do not have the luxury to simply get up and run away from the danger. If they want to survive, they have to employ a different strategy. For many, this involves the use of special chemicals called green leaf volatiles. These are released into the air and may fulfill a wide array of purposes. In some cases, they are meant to act as poison, damaging or even killing the enemy. For example, the acacia trees in Africa are known to fill their leaves with tannins as a way to stop giraffes from eating them. They also release a specific compound, which alerts nearby plants to the danger, so that they can prepare before they are themselves threatened. There are certain chemicals, which help to stimulate the growth of new cells at the damaged are, so that the wound may close faster and some, which even act as a type of antibiotic, preventing bacteria or fungi from infecting.
But by far the most extraordinary of their uses is as a distress beacon. Some plants have evolved special odors, whose sole purpose is to attract certain birds or insects, which are the natural predators of their enemies. This way they get a free meal and the plants gets rid of the nasty pest, which is bothering them. Which is exactly the case with our lawns. Damaged grass releases odors, which are meant to attract different caterpillar eaters. Among them is a group of hydrocarbons, including some aldehydes and alcohols, which cause the “green” smell to which we are accustomed to.
Sometimes the chemicals, released by plants have multiple purposes. For example, many plants produce nicotine, caffeine or mustard oil as a self-defense against insects. However, bees react to caffeine in a way, similar to humans and once they are used to it, they will continue visiting the plant to get their daily dosage. In return the plant is rewarded by being frequently pollinated by the helpful insects.