September Puzzling Phenomenon: Fairy Ring
Developed by Sarah Lamphier, September 2016
Ecosystem interactions and/or symbiosis
Introduction & Phenomenon
I had been stuck inside for a solid two days due to record-breaking rains and local flooding. When the rain stopped and I finally ventured out, I observed something perplexing in two separate yards in my neighborhood:
What could possibly cause mushrooms to grow in this neatly formed circle? One of the
neighbors was out walking her dog, and I asked her about the strange ring of mushrooms in her yard—she said the lawn was clear the day before, that they popped up overnight, and she did not “plant” anything there on purpose. In fact, she suspected that the ring had been left behind by fairies who had danced in a circle in her yard during the night. I nearly laughed out loud, but she insisted and explained that she had a family heirloom painting of this phenomenon hanging in her house:
Do you buy her fairy explanation? If not, what do you think caused these rings of mushrooms?
Explanation of Science Involved
Fairy rings are formed by certain varieties of fungus that flourish in wet, rainy conditions. The body of the fungus (called the mycelium) lives underground, and it grows outward in a circle in search of more and more nutrients. The mushrooms spring up from the edge of the mycelium, especially in wet weather, and therefore form a ring. The organism itself is actually a full circle, which is not at all a curious shape for an organism—but it appears as a ring because the only visible part is the perimeter that shoots up mushrooms above ground.
Additionally, fairy rings that form under the canopy of a tree and appear to neatly circle a tree trunk are typically evidence of a symbiotic relationship between mycorrhizal fungi that partner with tree roots (mutualism). The tree roots gain fixed nitrogen from the mycelium of the fungi and the fungi depend on the tree roots for structure and space for growth.
Other, less dramatic and more common instances of this same organismal interaction with the environment are circles of differently colored grass in a lawn—deep green at first, then dry and brown. As the fungus grows, it breaks down the dead organic material beneath the grass, which at first acts like a fertilizer and enables the grass to grow more richly than the rest of the lawn. But then the fungi uses up all of the organic material for its own growth, and in its absence, the grass at the perimeter of the mycelium dies for lack of nutrients.
Further ideas for classroom use
-Could be used to begin a unit on ecosystem interactions. After establishing context and showing the photos (fairy part obviously optional!), students could draw explanatory models of what they think is causing the growth of mushrooms in a ring. If used as a full-blown modeling exercise like we did with the broken wine glass during the summer, some gotta-haves for the later model iterations could include:
1. What exists beneath the grass to support fungi growth in this location?
2. What role does the rainy weather play, if any?
3. How are the mushrooms interacting with the tree (in the 2nd photo)?
4. (After showing non-mushroom circle photos, perhaps later in the unit), why does the grass first turn a rich green, followed by brown?
-Later in a unit on ecosystems, you could use just the tree photo and grass ring photos as a way to introduce symbiosis. After providing some basic information about what’s going on beneath the surface, possibly even showing or drawing a picture of the mycelium and tree roots, some key questions to elicit student thinking and help with sensemaking could include:
1. How are the mushrooms interacting with the tree?
2. What might the mushrooms “get” from the tree root system?
3. What might the tree roots “get” from the fungus?
4. Which organisms benefit from this interaction?
5. How does this interaction compare to _______? (Bring in another symbiotic interaction, but one that is parasitism or commensalism, such as ticks and deer or barnacles and whales.)