Roots of Relationship

Under the pine needles lies one of the secrets to forest health

The Pringle Falls Experimental Forest

The summer is warm and sunny in Corvallis, but my travels draw me east. Over and past the Cascades is an open land where the cold sparkling waters of a river flow north, and the sweet smell of Ponderosa pine blends with the fresh scent of lodgepole — the Deschutes National Forest. My one-person tent is packed in the back of a white state-owned pick-up truck with the essentials: a sleeping bag, a GPS unit, a camera, some protein bars, lots of buffalo jerky, a “Rite in the Rain” notebook and a pencil, a brown backpack, a bright orange hard hat and a soil corer.

In the late afternoon, I arrive at the Pringle Falls Experimental Forest and set up camp. The Forest Service cabins are nestled next to the gurgling and gushing Deschutes, whose French name means “River of the Falls.” The sounds of the rapids downstream bring a sense of calmness to my spirit. At the campsite, the ground is laden with pinecones, and the pine drops (Pterospera andromedea) expose themselves above the dead needles, branches and other forest litter. I unpack my gear and prepare for an early start out to the field sites the next day.

Mixed stands of Ponderosa and lodgepole pine dominate the Pringel Falls forest.

Mixed stands of Ponderosa and lodgepole pine dominate the Pringle Falls forest.

As you might guess, this isn’t the typical camping trip. I am embarking on an expedition. As a graduate student in the College of Forestry at Oregon State University, I am exploring something that lurks in the soils of Central Oregon — a fuzzy microscopic fungus that colonizes tree roots and might predict the future of the forest.

But why is the future of the forest at stake, and why dig underground when we are concerned about trees? The answer lies in the effects that organisms have on one another in a forest ecosystem. Like intricate underground machinery, fungi connect life-giving nutrients in the soil to roots that transport water and food to tree trunk, branch and leaf. Trees connect to climate and wildlife in an environment that evolves over time.

In the near future, scientists expect that climate will change and our forests will adapt. Tree zones will shift and a valuable tree species in the Deschutes National Forest — lodgepole pine (Pinus contorta) — is predicted to decline. This change will affect people as well. Native Americans used the long, straight and lightweight poles to build teepees. Today we commercially harvest lodgepole for telephone poles and fences. Big-game animals, such as deer and elk, use lodgepole as habitat.

Pine drop fungi

Pine drops

Researchers at Oregon State University suggest that, as the climate warms, lodgepole pine will decline in the Pacific Northwest by the end of the 21st century. As a result, Ponderosa pine (Pinus ponderosa) may be able to migrate into lodgepole zones. But this migration is dependent on the distribution or co-migration of mycorrhizae (fungi that live on tree roots), which are largely unexplored in Central and Eastern Oregon. The question is: Will this migration will be successful?

To answer that question, it helps to know a little about an ancient relationship. Scientists think that mycorrhizae, the fungus colonizing tree roots, evolved with land plants. Fungi and plants have been together since the Devonian period, which began more than 400 million years ago. External root fungi, otherwise known as ectomycorrhizae, form a sheath on the exterior of tree roots. These artful fungi form symbiotic, or beneficial, relationships with their host. Once colonization is complete, they send out filaments, which mine the soil for water and essential nutrients such as nitrogen.

Ultimately, it comes down to a trade that the tree host must submit to: The tree provides carbon, in the form of sugars, to the fungus in exchange for nutrients. The relationship is essential for the host and fungus to have the highest degree of success in the ecosystem — in this case, an ecosystem that I have the privilege to explore.

Getting to the core

The author takes a soil core.

The author takes a soil core.

The morning sun is bright in Central Oregon, but the air is cold and crisp. On my drive to the field sites, I can see the white peaks of Three Sisters in the distance. I pull the truck into the first site, take out my maps and venture out into the forest.  My leather boots softly crunch on the dried pine needles covering the soil. I pound my soil corer into the ground making sure to take a sample of the top 15 centimeters  (about six inches) of soil. I take in the smell of fresh earth, as I unscrew the metal corer to reveal a rich brown cylindrical soil core made up of pumice, fine roots and the mycorrhizae, too small to be seen with the naked eye. I dump the dirt, fine roots and all, into a Ziploc bag and place it in my backpack for analysis.

In the lab in Corvallis, I use molecular technology, such as DNA tests, to identify the root fungi of Ponderosa and lodgepole pine. I extract DNA, compare it to mushroom DNA in a database and identify the suspects. Like a detective, I name the species and unearth the world that had lain unexamined beneath the soil. And suddenly, this underground community is less of a mystery.

Russela

Russula

Cortinarius

Cortinarius

My analysis reveals a diversity of species: Cenococcum, a black crusty fungus that doesn’t form mushrooms; Rhizopogon, which often forms subterranean truffles; and typical mushroom producers Cortinarius, Russula and Inocybe. It also reveals that the fungal community connected to Ponderosa pine and lodgepole overlap. That means that, when it comes to soil biology at least, Ponderosa will have a high chance of survival if it migrates into a lodgepole zone.

As the climate warms and the tree zones shift, the forest where we recreate and connect with nature may not be as we remember it. The warming climate might diminish one valuable member of the community, but forests know how to persist. By looking at underground fungi, we can determine whether trees have the potential to migrate into new zones and succeed. In the future, the smell of lodgepole pine might be absent from the breeze and the long skinny poles will be no more. Instead, the presence of underground fungi suggests that we might become immersed in the rich mahogany bark and sweet scent of Ponderosa.

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Editor’s note: Maria Garcia is a master’s student working with Jane E. Smith, research botanist in the USDA Forest Service. Garcia’s research is supported by the Forest Service and by a Graduate Research Fellowship from the National Science Foundation.

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