C12

Todd Arsenault
SCIENCE EAST

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In late summer I took an educational hike through a local woodland in search of mushrooms with a mycologist (a scientist who studies fungi) friend of mine.

Most of us don't think twice about mushrooms, apart from the few edible varieties available in the grocery store.

However, it turns out that fungi are astounding in their biodiversity and fundamentally important to the very survival of ecosystems.

During only two hours in the woods I estimated that we found about 40 different varieties of mushrooms. This included everything from finding small patches of chanterelles (a culinary delicacy) to walking through a hauntingly silent pine grove littered with dozens of the beautiful but deadly poisonous "destroying angel," which are so toxic that they aren't entirely safe to touch, let alone eat.

But I also found out there is a lot more to wild mushrooms than whether they are edible or poisonous.

The first question to ask yourself is "what are these things, anyway?"

Are they plants, or perhaps something else entirely? The mushrooms and other fungal growths we see are actually only the fruiting bodies of a much larger organism that inhabits the inside of a tree trunk or lives over a wide area underground.

These usually invisible parts are called the "mycelium," and are very much like the submerged part of an iceberg - a lot bigger than the bits you can see.

Despite the myriad colours of mushrooms, they are almost never green, because they are not plants: they lack the green pigment, chlorophyll, that grass and tree leaves have that allows plants to use energy from the sun and carbon dioxide from the air in their life processes (via photosynthesis).

As a result, fungi have to obtain their carbon molecules, generally in the form of sugars that can be used to provide energy or as building blocks to synthesize other molecules, from the soil, or more often from other organisms.

They can do this by feeding on dead organisms (in which case the fungi are called saprophytes) or by feeding on living organisms as either parasites or symbiotes. These latter two are basically the same thing except that the host is affected badly in the first case but actually benefits from the relationship in the second.

Many of the species we saw on our hike were saprophytes, such as wood rot fungi. These fungi play an important biological role by breaking down wood fibres from dead trees and returning carbon and nutrients to the soil in the form of humic material that is essential to maintain the structure, porosity and fertility of the soil.

Breaking down wood is not a trivial thing to do, biochemically-speaking, but fortunately for the forest, the wood rot fungi are expert recyclers.

We also saw many symbiotic fungi, such as "mycorrhizal" fungi, which are associated with plant roots.

When this occurs, the plants provide some of the sugars they've made by photosynthesis to these fungi, which in turn gives the plant roots nutrients like nitrogen and phosphorus the fungi have collected from the soil via their large network of mycelium.

Both parties benefit in this invisible and silent underground economy that trades in the currency of molecules. And perhaps even more surprising, many trees and plants, including some that humans cultivate for food, simply could not survive without their fungal trading partners.

At this time of year when we give thanks for the harvest, pause a moment to remember the many thousands of species of often-unnoticed fungi that play specialized and key roles in maintaining complex and delicately balanced ecosystems.

Their huge biodiversity is something to be thankful for, treasured and safeguarded.

Dr. Todd Arsenault is a volunteer member of the executive committee of Science East (www.scienceeast.nb.ca). He holds a PhD in chemistry. His column appears every fourth Wednesday.