Thursday, November 3, 2016
Mutualistic Symbiosis Between Mycorrhizal Fungi and their Hosts
By Cade Campbell
Though fungus has been drastically underrated throughout the centuries, it has played a vital role in the masked life of the ecological communities around the world. One example are the successional forests. The average forest today, in our area, has grown from a logged area. Recently logged areas are inhospitable for most moisture-loving organisms, including plants, insects and especially fungi, and once they leave, all of the other animals and plants cannot survive. So, the forest begins its succession cycle. Lichen has a part in this process using its own internal symbiosis, along with bryophytes. These tiny, unique plants and plant-hybrids begin to build up soil in raw, nutrient-deficient ground and even on xeric outcrops. Soon layers of ferns and herbaceous plants can begin to repopulate the area and trees seeds begin to arrive by wind or animal traffic. That’s when the fungi arrive. Almost simultaneously with the first white pine, carolina hemlock, red spruce or Fraser fir that sends a woody shoot smothered in waxy needles from the damp loam of the Appalachians, fungal spores start to form a mycelium amongst the future forest. A thick wad of strong, filamentous hyphae stretch into the dirt like a science-fiction monster to form a mycelium, and after a while they begin probing for a living host. However, they don’t want to harm it. You see, after the mycelium generates over several months to a full year, the seedling conifers become saplings and begin to learn the struggles of successional growth. Wind, cottontails, drought, extreme temperatures and competition lower the chances of survival. Until, that is, coniferous mycorrhizal fungus comes in. In a lot of elementary school science books, fungi are talked about only as the best example of a decomposer. But mycorrhizal fungi don’t really decompose waste, but instead, they form alliances. Saprophytic fungi already had their turn in succession and will again as decomposers after a previous forest is destroyed. So, after several days of searching, the hyphae attach to a pine. Every single mycelium across the expanse of the new forest area, joins with a partner tree. In the next few years, the saplings without mycelia beg for mercy as their gargantuan softwood brothers pierce the sky above. How can the mushroom-infected trees continue to grow in a healthier, happier state than their suffering counterparts? It’s a simple process. The mycelium shoots haustoria into the tree roots, which begin to exchange minerals from the soil that the mycelium collected for energy before connecting to another source, for photosynthetic energy flowing throughout the trees nutrient canals.
(Above: This is a Basidiomycete in the genus Cortinarius. This is mycorrhizal in riparian mixed forest, so it has many hosts. It reflects the energy it retained with strands of a silky cortina, the mushroom’s namesake, a spider-webbed hymenium-guard that protects its sporophytes as the primordium mushroom matures. This mushroom’s hyphae connect to deciduous trees, so it is final succession species. You could see the dead pitch pines and hemlocks in the same woods as this mushroom by the lake at Steele Creek Park.)
But as this exchange takes place, new trees pop up amongst the mature conifers. These trees are the deciduous hardwoods. They seem to be perfect additions to the myceliums’ hosts, but they grow untouched by previous myceliums. Instead, new fungal spores travel through the air and begin doing their work on the hardwoods. Like the fungus on the conifers, these species of fungi create myceliums and start symbiosis. But after a while, catastrophic events begin to happen between the mycorrhizal relationships of a forest. The hardwoods and softwoods start crowding each other out, but both are fueled by powerful mycorrhizal minerals. However, the biggest problem in the mycorrhizal relationships as the forest becomes more diverse is that different species of mycorrhizal fungus don’t get along. Fungal warfare between fungus is high tech and strange. You see, mycelia need their hosts to grow bigger and healthier than all of the other mycelia’s hosts in order to survive. So, the battle begins in the cool, wet soil of the forest, below the seemingly tranquil forest floor where plants and animals thrive. But the future of the trees relies on the unknown, underground battle that is about to begin. A fungus such as Tricholoma portentosum, or Marvelous Tricholoma may extend a few hyphae towards the soil’s surface, farther from its beloved brother; the white pine, to grow reproductive fruiting bodies above the leaf litter, when it comes in contact with a symbiotic Pleurotus ostreatus, or Winter Oyster Mushroom’s mycelium that is attached itself to a small red oak. As soon as the two cellular threads collide, both shrivel back and create defenses. Small, chemical daggers called messenger crystals are inserted into each fungi as warnings, and they release harmful, lacerating chemicals. To escape maximum damage from the messenger crystals, each fungus creates a chemical “barbwire”, a barrier that blocks the advancing mycelium. However, nature has already dictated which will win. The one symbiotic fungus, with its relationship cultivating the deciduous hardwoods always beats the conifers’. One by one, battle by battle, the conifers turn into spiky lodgepoles piercing the sky, leaning against sturdy hardwoods, or lying fallen sideways in the moss of the forest floor. And still today, if you walk through a Central or Southern Appalachian hardwood forest, you can see the purple, spider-webbed cortinarius, marvel at the enormous jeweled caps and velvet rings of the towering amanita, smell the fruity scent of the golden chanterelle, and taste the fall armillarias; and all who appreciate the woods should remember how God gave the lowly mushrooms their jobs as the farmers of the forest.
(Below: Fomes fomentarius, the Tinder Polypore, is farming the forest by removing the old, wet and rotten yellow birch tree amongst the U.S. Forest Service’s maple sugaring groves, where pipes feed from the trees throughout acres down to the collection tank near Mount Rogers. This birch is valuable for arboreal cavity-nesting bluebirds, owls and Carolina flying squirrels, but it is also valuable fertilizer for the new trees of the forest and food for mushrooms, bacteria and digging beetles. Even though it is saprobic now, Fomes fomentarius mycelia can become mycorrhizal and create a symbiosis with the surrounding maples once the birch is digested. This fungus gets its name from the Native Americans, who used the warm, fuzzy felt inside the dried fungus to keep an ember alive for hours while starting a fire.)
Stamets, Paul. Mycelium Running: How Mushrooms Can Help Save the World. 2005. Ten Speed Press.
Roody, William C. Mushrooms of West Virginia and the Central Appalachians. 2003. University Press of Kentucky