Photo by Laurie Campbell/NHPA

Make Way for Mushrooms

They do everything from protecting plants against parasites and disease to alleviating droughts. Now scientists are using mushrooms to fight global warming and clean up contaminated sites.

by Mary M. Woodsen

Red squirrels are always fussing about something. Just now one was directly overhead, its strident, staccato chatter bidding me a hasty adieu. But I'd tuned it outmy eyes were on the ground. It had rained for three days running. Now the sky was blue, the warm scent of autumn was in the air, and, thanks to heavy rains, mushrooms were fruiting by the bucketful. Ivory-hued oysters, tawny-brown honey mushrooms, orange fly agarics, and purple-tinged russulas were all out in force. I bent to loosen a huge clump of oystersone of manyfrom the base of a dead sugar maple. Whop! Something glanced off my head and shattered; a flurry of flakes showered all around me.

For a moment I was startled. Then I realized what had happened. It's a great field identification trick: Toss a mushroom against a rock, a treeor somebody's head. If it bursts apart, it's a russula. And what loves russulas, or most any other mushroom? Bugs, slugs, snails, chipmunks, mice, deer, and, of course, squirrels.

Red squirrels have beaned me before, though with spruce cones. So why not with a mushroom? And just now they had plenty of ammunition. Red squirrels harvest mushrooms, lay them across branches to dry, then cram them into their pantries.
There's good reason to celebrate fungi, beyond their culinary credentials. They protect green plants from parasites and disease, build soil, help prevent floods by making the soil more permeable, and alleviate droughts by siphoning water from inaccessible areas to the roots of plants.

Indeed, each mushroom we see is merely the fruit of an organism that's all but invisible. Beneath the cap and stem, weblike filaments, the mushroom's mycelium, spread through the soil, a dead log, or other substrate. Some fungal organisms occupy a world as small as the body of a fallen ant or an athlete's foot; others might permeate as much as 2,000 acres of forest. Yet for the most part fungi live unseen until the rains come and densely packed bundles of mycelia balloon forth as fruiting bodieswhat we, squirrels, and other creatures like to eat.

From the tropics to the tundra, from the tomatoes in your garden to the oak tree in your backyard, almost every plant that lives does so largely because of relationships with root-dwelling, or mycorrhizal, fungi that provide it with water and nutrients while keeping disease-causing pathogens at bay. It's even possible that green plants would not have evolved without mycorrhizal fungi. When plants washed out of the seas, they already excelled at turning solar energy into carbohydratesbut they had no experience dissolving nutrients from gravel and grit. Fungi, with vastly finer food-finding filaments (the mycelia may contain up to 50 times the absorbing surface as an equal mass of roots), made great helpmates from the start. "When plants climbed onto dry land, they quickly enlisted fungal partners that have been with them ever since," says Kathie Hodge, a mycologist at Cornell University.

And perhaps the harsher the environment, the greater the need. Boreal forests seem lacking in diversity, yet their handful of tree species may collectively associate with hundreds or even thousands of mycorrhizal species. It makes sense, says Sari Timonen, a mycologist at the University of Helsinki. "To use the soil most efficiently, a homogeneous tree population apparently needs more types of fungi to do the job. In Finland, where we have few tree species, Scots pine associates with at least 300 fungi."

Recently, Sara Wright and graduate student Kristine Nichols, soil scientists with the Agricultural Research Service in Beltsville, Maryland, discovered that glomalin, the substance that covers the mycelia of mycorrhizal fungi, is constantly being sloughed off into the soil, where it can remain for decades without decomposing. Because glomalin accounts for 27 percent of carbon in the soil even as it helps soil granules hold on to their carbon, it serves as a corrective for global warming.

Dung, dead animals, desiccated plantswe'd be over our heads in no time without a panoply of saprophytic fungi, such as the aptly named turkey tails and horse's hoof mushrooms. Fungi get their energy by secreting enzymes and other substances that break down surrounding organic molecules into smaller ones, which they then soak up. The oyster mushrooms on that dead maple I found were part of a complex, ever-changing community of fungi that collectively turn a dead tree into rich, soil-building humus.

But the magic of mushrooms goes beyond decomposing nature's garbage and helping plants grow. Now it seems they may even be the world's greatest cleanup crew for toxins. Mycologist Susan Thomas of the Pacific Northwest National Laboratory, in Sequim, Washington, recently led an experiment that used specially conditioned fungi to treat petroleum-contaminated sediment taken from a wetlands in Oregon.

A gritty array of industries lines the Willamette River there, and chemical contaminants have leached into the river. Thomas's site was a property once used to process and transport petroleum hydrocarbons. The mix of benzene, toluene, ethylbenzene, and xylenechemists call it BTEXthat had seeped into the sediments averaged more than 2,500 parts per million, far above the legal limit set by the Environmental Protection Agency (EPA).

Thomas's fungi had been carefully "trained" (the patent is pending) to consume toxic petroleum hydrocarbonsthe main ingredients in fuels and most pesticideswith gusto and speed. Wearing hazardous-duty gear, Thomas and a colleague, Meg Pinza, climbed into a metal bin about three times the size of a standard dumpster, where they made a compost heap of sorts by placing thin mats of fungal mycelia between layers of contaminated sediment. Thomas left the mix to its own devices for six months, although she returned monthly to see how the fungus was dealing with all that dirt. On several of those trips, flushes of mushrooms decorated the uppermost layer. Previous experiments had indicated that the mushrooms would be toxin-free. After six months the sediments had turned into a pleasantly loamy, organic soil. Best of all, the BTEX levels were reduced by more than 90 percent, to well below EPA limits.

"Remediation can involve lots of expensive options," says Thomas. "You can ship contaminated soil to a remediation facility or seal it up forever or dump it at sea. But these native fungi are completely natural and portablethey can go anywhere. They can enrich the soil, and there's no noise, no smell, while the cleanup goes on."

It wasn't the first time Thomas had worked with a fungal detox agent with so much muscle and oomph. In 1998 she headed up a group that treated heaps of oil-soaked earth at a highway maintenance yard in Bellingham, Washington, with a carefully selected strain of oyster mushrooms. These mushrooms were developed by mycologist Paul Stamets, who runs Fungi Perfecti, a Washington-based company that cultivates and promotes mushrooms.

How does Stamets persuade his fungi to feed on such a toxic brew? "I starve them," he says. "The fungi on a dead tree have other nutrients available to them, which is one reason it can take decades for a tree to decay. But I don't give these fungi any other foods, so it's eat or die. Some strains don't make it, others limp along, and some of them become prodigious petroleum-digestion machines." Dangerous as they are, these hydrocarbons are similar in molecular complexity to the wood fibers in treeslike that old dead sugar maple where the squirrel had beaned me.

Stamets calls these underground fibers the original World Wide Web. "The health of the planet is controlled by mycelial networks," Stamets says. "Where there are catastrophes in nature, we find that the solutions are literally underfoot." That's why Stamets is launching a new company that will use mycotechnology to clean up wastes. He is, for example, enlisting mushrooms on several salmon restoration and protection projects on the Olympic Peninsula. And, he adds, "we hope to create nonprofits to work in areas where the devastation is extreme but local economies can't handle the costs and polluters won't step up to the plate." Stamets is even developing fungi that break down nerve gas and other chemical-warfare agents.

Yet pervasive and adaptable as mushrooms are, they, too, can be threatened. If petroleum products don't faze fungi, other things can. In much of Europe, up to half of all mushrooms have vanished entirely, many of them the mycorrhizal fungi that protect and provide for trees. Collecting probably isn't a significant factormushroom hunting has always been a traditional pastime. Indeed, the declines are just as dramatic for inedible and poisonous species. Nor does poor forest management seem to be the cause. The mushrooms in question had survived the centuries as European forests were manicured or repeatedly logged. The culprit? The largest declines seem to be in areas of heavy air pollution.

Stamets has gone one step further by creating the Mushroom Genome Mycodiversity Preservation Project, to study and protect Pacific Northwest fungi. Many fungi are endemic speciestied only to specific ecosystems. At least 80 of them live only in the Northwest's old-growth forest. Of this group, the noble polyporea massive fungus that easily spans six feetis the first mushroom on an endangered-species list and is known to live in fewer than a dozen locations.

I was back at the dead sugar maple two weeks later. It had turned dry, and the pickings were thin. The honey mushrooms and russulas had rotted, and the last of the amanitas were bug-ridden. The oysters on the maple seemed to be gone. But at 10 paces the picture resolved itself anew. I realized that what I'd seen as dead flakes of bark were really dried mushrooms preserved in crisp, ivory splendor: oysters in their prime. Rain was in the air, and I knew that beneath the leaf litter dozens of incipient mushroomsnubs of tangled, densely packed mycelialay ready to surge forth with the next good soaking.

Mary M. Woodsen writes about nature from her home in New York's Finger Lakes.

© 2002  NASI

Sound off! Send a letter to the editor
about this piece.


Enjoy Audubon on-line? Check out our print edition!



The Nature of Fungi

Between plant roots and fungi, natural selection has favored an ingenious, intimate association in which the roots of pine seedlings are colonized by the mycorrhizal mycelium of the fungus Suillus bovinus. Surprisingly, roots are coarse structures, ill equipped to explore the soil for essential nutrients. The filamentous threads of fungi, called hyphae, forage for phosphorus and nitrogen for the roots; in exchange, the fungi receive sugars from the plant. Most forest trees get these nutrients via this symbiotic relationship, which works best when it associates with as many roots as possible. Indeed, the mycelium of a single fungus can colonize and interconnect many individual trees, as well as different species.

David J. Read