Fungi make up incredibly important part of plant ecosystem

Living on Earth

Sulphur Tuft fungus (Photo courtesy of the Encyclopedia of Life.)

Lynne Boddy, an ecologist from Cardiff University in Wales, is shuffling through the leaves in a little patch of forest in Concord, Massachusetts.

She’s spotted a soft birch tree log lying on the forest floor. She kneels down and starts tugging on the log.

Can you see this, she asks. 

"This," is a few limp, cream‐colored threads descend from the rotting log and make their way into the soil. They look a bit like plant roots, but are something else entirely.

"What we’re looking at is the main part of a fungus. Most of us think of fungi as things like mushrooms and toadstools. But that’s just the tip of the iceberg," Boddy said. "That’s the fruit body, and the fruit bodies are like the flowers of flowering plants. There’s another part of the fungus — it’s usually hidden in rotten wood and in the leaf litter on the forest floor."

These fungal threads, or mycelia, are doing the work of decomposition, slowly digesting and feeding upon this birch tree. One example is the sulphur tuft fungus, properly known as Hypholoma fasciculare.

An organism that grows both in the United States and in Britain, Boddy gingerly holds its mycelium and begins tracing it through the soil.

"Oh my goodness! It’s attached to an acorn from this oak tree. So it’s not only decomposing the wood of the birch tree, but it’s decomposing this old acorn," she said.

A little farther along, the fungal threads have grabbed a hold of another little acorn hat, crawled along its perimeter, and surged out the other end in search of something else to colonize — a branch, a tree stump, or another log. Nutrients consumed in one part of the fungi get routed into this vast, interconnected mycelial network.

And if one part of the network gets chewed up by a wood louse, say, or stomped through by a deer, it’s no big deal for the fungus. It’s so interconnected that there’s little risk of chopping one of these fungi in two.

Boddy loses the trail when the mycelia plunge straight down into the soil. But this fungal tapestry doesn’t just carpet the forest floor.

"All of these trees that you see around us, there are fungi within the trunks and branches, not doing very much – just tiny, tiny, little pockets," Boddy said. "And then the minute that the water in the sapwood of these trees stops flowing, these fungi will grow into bigger mycelia and start the decay process."

So, really, she said, even before the tree comes down, the decay process will have already started.

The question will be which fungus will succeed in making the dead tree its buffet. The fungus already in the tree will have a head start, but other fungus spores will waft through the air and still more will be waiting on the forest floor when it finally falls over.

That’s one portrait of the fungal community – lying in wait, wood‐thirsty, and skirmish‐ prone. But there’s another side to fungi. 

"None of these plants in this beautiful woodland would be here if it were not for fungi for two very good reasons. One is that the fungi, which are decomposing, actually release the nutrients that are locked up," Boddy explained. "And the second reason is that all of these plants, every single one of these plants around us have fungi attached to their roots."

These mycorrhizal fungi — species like Amanita brunnescens here in this woodland — associate with 90 percent of the plants on Earth. They ensheath the roots. Or sometimes they grow in between root cells. These fungi absorb water and nutrients from the soil, and share them with the plant. In exchange, the fungi get some of the sugars pulsing through the plant roots.

"It’s plants plus fungi that make the ecosystems of our planet work," Boddy said.

So, while it's easy to think of plants as just needing a little sun, a little water, and presto, it's not quite so simple. Boddy says, without fungi, we wouldn't have plants at all.

In fact, Boddy says that plants needed fungi to be able to colonize land 450 million years ago. So fungi both nourish and destroy. They pump vital fluids rich with nutrients into the very ecosystems that other fungi will later carve up and consume. They digest the dead, leaving behind the raw materials for new life to be born.

And it just takes getting your hands a little dirty to trace the weave of their vast network.