Tuesday, April 06, 2010

The Living Constellations Beneath our Feet

“. . . There is some kind of electrochemical communication between the roots of the trees. Like the synapses between neurons. Each tree has ten to the fourth connections to the trees around it, and there are ten to the twelfth trees on Pandora”.

So, says Grace the scientist (Sigourney Weaver) in an effort to explain the near mystical interconnectedness of that fictional planet in the movie Avatar. Being a scientist she wouldn’t use the word “gazillion”, but that is how you can interpret those numbers, quantities so huge that they are hard to grasp.

Pandora isn’t the only planet where trees are interconnected; you need go no further than your own backyard. I am not just talking about those intangible connections between plants and their animal pollinators, and plants and their animal seed dispersers. And I am not speaking of the soil enriching organisms that fix nitrogen to the benefit of many plants. These and others are important links in the web of life; but, in addition to those, there are physical, intimate, direct connections between plants and certain kinds of fungi. Moreover these fungi can establish connections between the roots of different plants. These extraordinary organisms are called mycorrhizae (or if you prefer mycorrhizas). The word mycorrhiza comes from two Greek words, myco, meaning fungus (fungi in plural), and rhiza, meaning root.

Take a look at mushrooms, those delicious morels or boletus or the deadly Amanita; you see them scattered through the forest. They look like a very small component of the plant community compared to the trees that tower over your head. Each of those mushrooms is a “fruiting body”, similar to a fruit, except that it produces spores rather than seeds. The mushrooms are the visible parts of a very large organism buried underground and called a fungus. Imagine an apple tree where only the apples are visible sprouting above the ground while the whole tree is spreading its branches underground. Such an “apple tree”, the main part of the fungus, is a very peculiar kind of organism, not as solid as a regular tree; instead it is made of a very intricate web of thin threads spreading out and connecting with themselves again and again when they meet, like a huge tridimensional spider web. They also link with the roots of trees, wrapping around them and penetrating their bark.

Fortunately, mycorrhizae are beneficial fungi which do no harm to plants; instead they establish a partnership with them. With their numerous threadlike tendrils they absorb water and mineral nutrients from the soil more efficiently than roots; so they can transfer these to the plants. In return, they get the sugars and vitamins that the plants synthesize thanks to their chlorophyll and with the help of the sun. It is a cooperative venture that benefits both partners.

Other mycorrhizae never see the light of day; they produce their spores underground and don’t form mushrooms; as a consequence, most of us are totally unaware of their existence. They are perhaps more abundant and more important to the life of the plant communities than the ones that produce mushrooms. Some of them penetrate the very cells of roots establishing an even more intimate connection with their partners.

Some members of the vegetable kingdom don’t require this kind of help. But it is estimated that at least eighty per cent of all plants are dependent on or benefit in some degree from mycorrhizal associations. It is a very ancient contract between plants and fungi, at least 400 million year old existing long before there were dinosaurs roaming the planet. It is possible that the partnership is even older and that it was established when the first pioneer plants left the water and climbed on land, around 425 million years ago.

You may think at this point: “very interesting, but how does it compare with the planetary network in Pandora?” This is what I am getting to. All these hair-like tendrils are capable of recognizing the members of their own clone and also those of closely related clones when they come in contact. They fuse when they meet, to the point that they become like one. Thus they connect among themselves and they reach out to the roots of trees, not just one tree but several. They do it again and again, forming countless links. This is the “Wood Wide Web”, so called by those who study these relationships. The bridges they form are capable of carrying water and minerals and even other nutrients not just from fungus to plant and vice versa, but also from tree to tree. Thus a fir tree connects to another fir tree and also links to the birch tree beyond them. When you walk in your vegetable garden, little do you know that the leek is talking to the carrot using the unseen web right under your feet!

A field that gets plowed over every year and is cultivated with annual crops has to start from scratch building this network every year, but a forest possesses a network perhaps as old as its oldest tree. Thus, the majestic old tree, surrounded by younger ones becomes a hub, from which the fungal network radiates in all directions like the spokes of a wheel maintaining continuous communication among all its parts. It makes you think of “Home tree” in planet Pandora or of a wise old elephant matriarch ensuring the safety of its herd.

But it is really the mycorrhizae that are the stewards of the forest. They seem to sense where the pressing needs of a plant are and from where they can borrow. In the spring, when the birches are leafless, the mycorrhizae take nourishment from the firs and carry it to them. Later on, when the leaves of birches cast shadow over the fir trees and these need some food the web reverses its flow, providing nutrients to firs taken from the birch.

“That is more connections than the human brain” explains Grace “It is a network, a global network”. And so it is with these obscure fungi; each mycorrhizal community nurtures one patch of plants and it contacts loosely with surrounding communities throughout large tracts of land. They confer resilience and stability to the forest far beyond what the trees could do by themselves.

When I ask people I meet what the word fungus means to them, the most frequent answers are “disease”, “plant damage”. The answer should be “connectivity”, “cooperation” or “healthy plant communities”.

List of articles
Squirrels, Managers of the Forest