Monthly Archives: September 2016
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.
By Bruce Rottink, Volunteer Nature Guide and Retired Research Forester
With the exception of a few “iron eating” bacteria described in my Naturalist Note of May 3, 2015, all life at Tryon Creek State Natural Area (TCSNA) depends upon energy from the sun. It might have to go through several steps like plants using sunlight to create carbohydrates, insects eating the plants, birds eating the insects and bigger birds eating the smaller birds, but eventually we all depend upon the sun.
How Much Sunlight Is There?
The amount of sunlight falling on TCSNA depends upon many things. It depends, for example, upon the season of the year, the time of day and the amount of cloudiness. An important factor for the plants includes competition from other nearby plants. So how much sunlight is there in various parts of the forest?
To find out, I took measurements at TCSNA on two totally clear days, July 13 and July 30, 2016. On July 13th, I focused on an area near the Nature Center around noon, and on July 30th, I focused on the Cedar Trail in mid-afternoon. On July 13th, the full sunlight at noon in the Equestrian Parking Lot measured 104,000 lux (lux is a standard measure of light intensity). On July 30th my 2:50 PM and 3:30 PM full sunlight readings averaged out to 101,000 lux.
Out on the trail, 3 feet above the ground, there were about 1500 lux of light on July 13th, and from 260 – 610 lux on my second day in the forest.
How dark is “shade”?
I plunged into the “dark side” by measuring the light level under some plants. First I checked under a dense clump of salmonberry (Rubus spectabilis). At the soil surface there were only 60 lux of light under those plants. But the champ was a cluster of young western redcedar (Thuja plicata) which let just 50 lux of light through to the soil surface. That is less than 1/20 of 1% of full sunlight. And what was growing under that clump of western redcedar? Take a look in the picture below:
Almost nothing grew under this clump of western redcedar.
Why Don’t Plants Grow in Dim Light?
Plants use light to power the photosynthetic process to produce the carbohydrates (like sugars) they need to grow. The more light, up to a point, the more sugar. So you would think that they might grow everywhere there is any light at all. However, the flip side to photosynthesis is respiration. Respiration is the result of internal processes for cell maintenance that are vital to life. The amount of light at which the process of photosynthesis is creating the same amount of energy that the plant uses to maintain its basic functions is called the “compensation point.” At this point, the plant can stay alive, but not grow. When the light level is so low that photosynthesis falls below the respiration rate, the plant ultimately dies.
Various species of plants have different compensation points. Plants are sometimes grouped by their tolerance of shade. At TCSNA one example of an “intolerant” plant (one that can’t tolerate the shade) is our Douglas-fir (Pseudotsuga menziesii). While we have many mature Douglas-fir, the number of young ones is very small. Shade tolerant plants include both the western redcedar and western hemlock (Tsuga heterophylla).
Published standards on how many lux plants need are somewhat variable. As a general rule it appears that shade tolerant plants need at least 150 to 500 lux, while shade intolerant plants need at least 800 to 1500 lux to survive. On the high end, it appears that for all plants about 25,000 to 35,000 lux saturates the photosynthetic process.
Those Mysterious Sunflecks
Both days at the park I periodically encountered “sunflecks” on the trails beneath tall trees as shown in the picture below. They typically appear as circles or multiple overlapping circles.
The first day, the light intensity of these sunflecks typically measured between 2,500 and 9,000 lux. That is the equivalent to about 2-1/2 to 9% of full sunlight. My second day measuring sunflecks at approximately 3:00 PM, the majority were from 2,500 to 3,500 lux. So these sunflecks can provide adequate light for photosynthesis to the plants near the ground.
Sunflecks have intrigued me ever since I was delivering newspapers during a partial solar eclipse in Minneapolis, Minnesota in the early 1960s. I saw something on the side of a house that stuck with me the rest of my life. Four decades later, during the partial solar eclipse of June 10, 2002 at my home in Lake Oswego, I captured this phenomenon on film. The photo below was taken during a partial solar eclipse. This is how the sunflecks looked on the side of my house.
Amazingly, the sunflecks were crescent-shaped, not circular. Compare the sunflecks above to the diagram below of what the sun (and moon) looked like that day during that partial eclipse (based on information from the internet).
You will note that the sunflecks on the house seem to be flipped 180° from the sun’s actual shape in the sky. This is because of the sun’s image passing through a tiny hole in the crown of the tree. This is sometimes referred to as the “pinhole camera effect” as illustrated below using a tree instead of the sun. This effect was described by Aristotle in the 4th century BC.
Interestingly enough, your eye also does this, and the images on your retina at the back of your eye are all upside down.
Flipping the image of the actual eclipse by 180° we get the following image, which is virtually identical to the images on the side of the house. This is because the tiny spaces in the crown of the tree are acting as pinhole cameras.
The bottom line: the round sunflecks we see on the trail are really images of the sun.
Why aren’t all sunflecks the same?
Sunflecks have two different properties, size and brightness. Both of these properties are influenced by two factors. First, the size of the hole in the canopy, and second, the distance from the hole in the canopy to the ground. For a given size hole in the canopy, the closer to the ground, the smaller and brighter the sun fleck. In the picture below, the sunflecks are produced by the same size hole. Because both holes are letting the same amount of light through, the larger sunfleck doesn’t appear as bright as the small one.
For holes in the canopy at the same height above the ground, the bigger the hole, the bigger the sunfleck. Both sunflecks below are produced by different size holes at the same distance above the ground. However the intensity of light in the sunflecks is the same.
If you start thinking about the combination of different size holes at different distances from the ground, you can see that a vast array of different sunflecks are possible.
So in a sense, these sunflecks on the trail are constant reminders that the sun is indeed the mother of us all.