Fungi: The Amazing Ancients
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
Fungi (singular = fungus) are one of the oldest types of living organisms on earth, dating back approximately 1 Billion years. It may be slightly easier to grasp if I say that fungi have been around approximately 12 times longer than the earliest primate ancestors of humans. The fungi have used their time to develop diverse, and sometimes complex lifestyles!
The basic building block of fungi is a hypha (plural = hyphae) which is basically a long branching fungal thread. They can be seen in the picture below. This growth was on the underside of a leaf that was lying on the damp soil. The hyphae are attached to both the cottonwood (Populus balsamifera ssp. trichocarpa) leaf and a Douglas-fir (Pseudotsuga menziesii) needle. The hyphae are sometimes collectively referred to as mycelium (plural = mycelia).
Fungi, unlike plants, do not make their own food. This has led many fungi to adopt one of three lifestyles; a) a decayer of non-living organic matter; b) a parasite/disease of living organisms; c) a helpful life-partner of another organism. All three of these life styles can be found at Tryon Creek State Natural Area (TSCNA).
Fungi as Recyclers
Fungi at TCSNA recycle (“decay”) many things, as pointed out in my Naturalist Note of October 2015. This can be thought of as their “rotting” function. This is nicely illustrated in the above photo, where the fungi are probably rotting both the leaf and the needle. Rotting releases nutrients in the organic matter to be re-used by other organisms. Unfortunately, some of the most obvious examples of this at TCSNA are fungi which are decaying dog feces (a. k. a. “poop”) left behind by dogs tended by those few people with apparently little regard for either the park or other visitors.
Fungi as parasites or disease
Attacking dead things is one lifestyle, being a parasite, or disease, is quite another. If you’ve ever had “athlete’s foot” you know first-hand about fungi causing diseases. Some of the fungi at TCSNA are diseases too. One tree disease is caused by the honey fungus (Armillaria mellea). They produce thick black shoestring-like structures called “rhizomorphs” under the bark of this log (see below) alongside Old Main Trail. Rhizomorphs are typical of the honey fungus. Species that are rated as “highly susceptible” to this fungal disease include our grand fir (Abies amabilis), Douglas-fir and western hemlock (Tsuga heterophylla).
Fungi as life partners
Sometimes fungi will form a close, often physically interwoven relationship with another organism that benefits both of them. A relationship that benefits both partners is called “mutualism” which is a specific type of symbiosis. One of the most common mutualistic relationships fungi form is with forest plants, including most trees. Fungi will grow on, or sometimes into, the roots of plants, forming structures called “mycorrhizae” (from the Greek “fungus root”).” Long fungal hyphae will extend out from the mycorrhizae into the soil. In this relationship, the plant provides the fungi with food (think “sugar”). In return, using chemical means the plant does not have, the fungi very efficiently extracts nutrients from the soil, especially phosphorus, and transports it to the plant.
Another advantage to the plant is that mycorrhizal fungal mycelium are dramatically smaller in diameter than the plant’s own roots. It takes less energy to build the mycelium than it would take to build its own roots. Thus for the same expenditure of energy on the part of the plant, it can tap into a much greater volume of soil by using the finer fungal threads. Over 2,000 species of fungus have been identified as potential mycorrhizal partners of Douglas-fir.
The coral fungus shown below is one of the fungi found at TCSNA that can have a mycorrhizal relationship with many tree species.
Another totally different kind of symbiosis, is when a fungus lives with an algae to form what we call a lichen. The fungus does a great job of providing moisture for the algae and the algae is able to photosynthesize (create sugar) which supports the fungus. There are thousands of species of lichen world-wide, but they have been grouped by their form into several different types. The fruticose lichen has lots of branch-like structures. The crustose lichen often looks like a thick layer of paint, and the foliose types have what looks like primitive leaves.
In the lichen, only the fungus reproduces sexually, and if some algae cells happen to cling to the spore as it floats away, great; otherwise, when the fungus lands, it will have to find some new algae with which to start a new lichen.
Fungi use chemical warfare
You don’t survive a billion years without picking up a few tricks along the way. Fungi have developed a broad array of chemical weapons in their fight for survival. Some fungi have been found to produce chemicals which inhibit competing organisms, like bacteria and other fungi, from growing near the fungus. Recall that the medicine penicillin was originally isolated from a fungus.
Some of these chemicals are also very effective in killing cancer cells. A chemical extracted from yew bark, taxol, has been known for years to effectively treat some breast cancers. Researchers have recently discovered that a fungus growing inside the yew bark, Taxomyces andreanae, produces the chemical taxol. Whether or not the yew tree itself also produces the chemical is not clear.
“By the sword you did your work, and by the sword you die”
The sentiment above, expressed by the Greek playwright Aeschylus in the 5th century BCE, applies to fungi as well as people. Just as fungi sometimes use chemical warfare against other organisms, sometimes chemical warfare is used against fungi too. TCSNA’s garlic mustard (Alliaria petiolata), an invasive plant native to Europe, produces and releases chemicals to stifle fungal growth. Since an overwhelming majority of plants are mycorrhizal, killing fungi interferes with the growth of plants that would otherwise compete with garlic mustard. Garlic mustard itself is one of a small group of plants that doesn’t have mycorrhizae.
One the principal chemicals released by the garlic mustard is allyl isothiocyanate. This chemical is released into the soil, and is toxic to the fungi located in the soil. Interestingly enough, in garlic mustard’s native Europe, the soil fungi are resistant to the garlic mustard’s chemical. Apparently our native fungi haven’t developed that resistance yet.
And sometimes life gets complicated!
There are a few fungi which have a lifestyle which is one of the most complicated of any organism on earth. These are called “heteroecious rust fungi.” These fungi are plant diseases. Their unique characteristic is that they need to use two species of plants to complete their life cycle. One of these fungal species that we may have at TCSNA is the “common fir-bracken rust” (Uredinopsis pteridis). This fungi spends part of its life cycle growing on bracken fern (Pteridium aquilinum) and the other part on grand fir.
I have no proof that we have this disease at TCSNA, but since we have both hosts here, it is a distinct possibility. Furthermore, this fungus sequentially produces not one, not two, but five different kinds of spores during its life cycle. Of the different spore types, some are produced only on the fern, and the others are produced only on the grand fir. Frankly, this complicated a life cycle boggles my mind. The two questions that plague me are: 1) How did this complicated life cycle ever get started? and 2) What conceivable advantage is there to the fungi in needing two hosts? The answers have eluded me.
The fungal internet
Human’s internet is a johnny-come-lately compared to the “internet” that fungi developed long ago. Strands of fungus often connect the root systems of two trees in the forest. The trees don’t even have to be the same species. The overall results is that fungi of one species or another, connect almost all the trees in the forest. Something like this:
It appears that fungi connect nearly every tree in the forest with other trees. While there is clear evidence that some small amount of sugars are passed from tree to tree, this fungal internet may have a far more interesting function.
Two different studies have found that plants apparently transfer “information” from one to another via their interconnecting fungi. In one study, some plants were deliberately infected with a fungal disease (not one that creates mycorrhizae). Researchers found that if a neighboring uninfected plant was connected via mycelium to the infected plant, it was dramatically less likely to catch the disease, than if the uninfected plant was NOT connected to an infected plant. It appeared that the mycelium was passing along a message that said, “Hey this disease is coming around, better get ready to resist!”
In a second study, the same basic effect was found when one plant was infected with aphids. The uninfected plants appear to get some signal through the mycelium from the infected plants, and its anti-aphid defenses kicked into gear before they were actually attacked by the aphids.
As you can see, the fungi of TCSNA are themselves complex and terrifically creative organisms. They play many important roles in our forest, by decomposing organic matter, acting as diseases, and forming mutually beneficial relationships with other organisms. They are the hidden partners in making our park a great place to enjoy nature.