So the long-awaited post on talking trees.
So how on earth does a tree 'talk'?
Plants have multiple ways of communicating, and the way they do it depends on what they're trying to communicate with.
For example, a flower that is long and red and tubular is a signal to birds that there is a tasty sugary treat awaiting them, similarly a rich-smelling fruit would indicate it's ripe and ready to be picked (or from the plant's point of view, dispersed), or a red one might indicate poison.
These are all fairly obvious forms of communication - we can see the flower and smell the fruit. But this isn't what is meant by a plant 'talking'. Besides, this is all communication with animals - what if the plant wanted to communicate with another plant?
There are actually a couple of ways this happens, one through the soil and the other through the air.
Many plants exude compounds from the roots in order for inaccessible nutrients in the soil to be altered to a form the plant can then use. These root 'signals' can be used by more scrupulous species as a way to block the root growth of other plants, or by parasitic plants to find their host.
But this isn't what we mean by trees 'talking' either.
Communication through the air, and hence the leaves, is known as the 'talking tree' effect. According to our anatomy 101, plants have pores called stomata on their leaves which allow the passage of oxygen and water into and out of the leaf. These molecules are able to move in the air, which as any school kid can tell you, is made up of other stuff too. This means any compounds small enough and light enough to move through the air can also enter the leaf, and can then be sensed by the recieving plant. So by releasing certain chemical signals into the air when they're attacked by herbivores, the plant being eaten can then warn other plants in the area that there is a threat around, and those surrounding plants can act accordingly.
Act accordingly?
What can a plant do about it?
Well they can't move, but they can act. Many plants synthesise toxins to discourage herbivores, but do so only when they're under attack. Because of this, most will still lose some leaf tissue before the synthesis of those toxins kicks in as they need to sense the threat first. So if they have the ability to sense other plants are under attack, they can pre-prepare themselves ready for attack, and minimise the damage done to them. Clever!
So what would be the point of this? Why would a plant bother to try to tell another plant there are herbivores in the area? Why not just make your leaves poisonous the whole time? The answers to this is: conserve your resources until they're needed. It uses resources to make toxins, as well as requiring some means of storing them, so why make them unless you need to? Many of these anti-herbivore compounds break down relatively quickly as well, so long-term storage wouldn't be a very good option. By listening in on other plants in the area, toxins can be synthesised only when they're needed, solving the resource and storage problems whilst still protecting the plant.
Cool, eh?
