Plants and their predators have been evolving in step with each other since the earliest mosses and ferns first grew on land. Covering themselves in spines or producing harmful chemicals is a pretty good defense, but plants are a lot more active in their fight against herbivores than many tend to think. Now, a new study has discovered that young saplings are able to tell the difference between whether or not their bud have been damaged by the wind or have been nibbled by a deer.
As a young tree stuck to the place growing on the forest floor, the ravaging appetite of a hungry deer could spell calamity, and ultimately the end. But the saplings don’t go down without a fight, launching a chemical defense against the marauding herbivores by producing astringent tannins that savour bad and set the beasts off. But the plant needs to know whether or not damage to its buds is indeed caused by a munching deer, or more benignly caused by other things such as gust.
It turns out that when a bud is damaged, the trees can sense the animal’s saliva in the meander. When it does, it triggers a reply from the sapling, which produces a hormone known as salicylic acid, that in turn causes the plant to increase the concentration of tannins in that the members of the plant. Not only that, but it also spurs the plant on to produce more growth hormones that cause the remaining buds to grow more vigorously, and make up for those that have been lost to the deer.
On the other hand, if a foliage or a bud snaps off without a roe deer being involved, the tree stimulates neither its production of the salicylic acid signal hormone nor the tannic substances, explains Bettina Ohse from the University of Leipzig, lead writer of such studies, published in Functional Ecology. Instead, it predominantly renders meander hormones.
The intricacies of how plants deal with being eaten by animals may astonish some people. Rather than being passive organisms that are predated upon, plants are actively trying to fight off their predators. One study, for example, found that plants can in effect hear themselves being eaten, and mobilize a chemical defense with a view to responding. And not only can plants sense when they are being eaten by insects, they can even then warn others nearby as to the damage that is being done.
Initially rejected as complete hokum, it now turns out that when an animal starts chewing on leaves, the plant produces what are known as volatile organic compounds into the air. These are then identified by other plants growing nearby, which respond appropriately to pre-empt the threat of being munched on themselves by increasing the concentration of unsavory chemicals, such as tannins, in their own leaves.
So next time you go for a stray in the great outdoors, bear in mind that while the trees and plants around you might looking serene and passive, they are actually waging a bitter warfare with the animal kingdom.