Garden Word of the Day
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Most of us have had the experience of discovering a forgotten something in the back of the fridge, or found a fruit in the bottom of a bowl, covered with fuzz. That fuzz is a type of fungus.
The white threads seen in soil and compost - more fungus. But there is far more to this bizarre life form than you might expect. Prepare to be blown away!
A different kingdom
We all know about the animal kingdom and the plant kingdom, but the kingdom of fungi is far less familiar. Fungi are not plants. In fact, they have more in common with animals than plants. Fungi broke off into their own group one billion years ago, and we have a lot to learn about them.
Fungi can cause and cure disease. They have been used as pesticides, poisons, and potables. They are the Earth's (and your garden's) primary decomposers and critical players in nutrient cycling and most food webs. Fungi are used in bioremediation and there are fungal spores drifting down onto your skin as you read this.
Fungi spoil our food and help it grow. They break down our buildings and provide us with building materials. Every step that you take on soil impacts approximately 300 miles of fungal threads. Every step. Three hundred miles.
There are species of ants that farm fungi for food. One type of wasp injects her eggs together with a certain fungus into the bark of host trees. The fungus starts to rot the wood, making it easier for her babies to eat when they first hatch. There are fungi living in the gut of several garden insects, including beetles and cockroaches.
Once we begin to see fungi for what they are, an extremely large, diverse group, I think we can appreciate them more fully.
The fungal family
Yeasts, molds, and mushrooms are all types of fungi, while slime molds and water molds are not. Water molds (oomycetes) are more closely related to algae, while slime molds (mycetozoa) are closer to amoeba. [Did you know that lichens are actually mutually beneficial communities of fungi and algae?]
Scientists estimate that there are millions of species of fungi. So far, we only know about 150,000 of those. An area of fungi is called its mycobiota. The study of fungi is called mycology. There are currently nine types of fungi that have been identified. You can look them up, if you're into that sort of thing, but this post is already packed with a lot of information.
One thing that makes fungi different from plants is that their cell walls contain something called chitin. Chitin is also found in fish scales, squid and octopi beaks, and insect exoskeletons. Plants do not contain chitin; they have cellulose. Some types of fungi have structures called rhizomorphs, which behave similarly to plant roots.
Fungi grow threadlike structures called hyphae. These are not chains of cells, the way algae grow. Instead, hyphae are tubes that may hold several nuclei. Hyphae grow at the tips of these tubes and often branch. Collectively, these hyphae are called mycelium. Mycelium are found in all of Earth's soil. Growths of mycelium are called colonies. There is one fungal colony in Oregon that covers 2,400 acres and is believed to be 9,000 years old. Known affectionately as the "Humongous Fungus", this specimen of Armillaria ostoyae may be the world's largest living organism, when measured by area.
Fungi do not perform photosynthesis. Like animals, they must get their food from other living (or dead) things. The different ways fungi gather their food may surprise you. In some cases, fungi do this by dissolving organic material using digestive enzymes and absorbing nutrients. Other fungi, especially pathogens, have piercing structures that can break through plant tissues, spreading disease. More on that in a minute.
Some fungi are miners. They secrete acids that dissolve tiny rocks, creating tunnels, and then harvest and store those minerals for later use.
You've probably heard me talk about mycorrhizae. Mycorrhizae are microscopic fungi that live in and around the roots of many garden plants, helping them to absorb important nutrients. These fungi also help transport inorganic, mineral nutrients from one plant to another, in exchange for sugars produced through photosynthesis. There's a great NPR radio show, From Tree to Shining Tree, which talks about an experiment that showed how trees share their food with other trees, even trees of different species. All of this happens because of soil fungal colonies. But there's more to fungi than simply decomposing and mining.
There are fungi that actively hunt springtails and other microorganisms found in the soil. They trap their prey in sticky nets and insert hyphae into living insects and nematode eggs, sucking out the innards. But they don't keep all of that food for themselves. Fully one-fourth of those insect guts and embryos end up in nearby trees. In exchange for that gift, trees give 20-80% of the sugar they produce through photosynthesis to the fungi growing in and around their roots. The fungi, in turn, hold that sugar until it is needed by the tree, or its neighbors, at which time they give some of it back.
We now know that trees send chemical messages through these fungal networks, warning neighboring trees of illness, or insect or herbivore attack. We also know that dying trees move their resources into the fungal network to be shared with other trees. We do not know who or what decides the movement of these resources or chemical messages, but I can't help wondering about the neuron-like structure of the fungal networks that help keep our plants alive. But I digress...
Fungi use several methods of reproduction and some species use more than one method. In most cases, fungi reproduce by releasing spores into air or water. A few older specimens have spores with wiggly tails called flagella. Most fungi now use cup-shaped fruiting bodies, called apothecium, which are lined with a tissue that produces spores. Spores are often ejected forcefully, with the initial force reaching nearly 10,000 g's!
Fungi also reproduce by splitting off bits of mycelium, while others use colors and odors to attract insects, which help distribute spores. Most spores are spread on wind, which is why a fungal disease in your neighbor's yard is a problem for your garden.
Fungi in the garden
Fungi perform several functions in the garden: some of them good, and some of them not so good. Fungi decompose our compost piles and provide many garden plants with nutrients. Some fungal species inhabit the leaves and stems of your grass family plants, making them less attractive to herbivores and better protected against environmental stresses in exchange for room and board.
One Swedish study even showed that it is fungi and not plants who are sequestering the majority of the carbon held in northern boreal forests. But all too often, fungi are the cause of plant disease.
Fungi as disease carriers
There are many different fungal diseases that can affect garden plants: black spot, blights, downy and powdery mildews, rusts, and wilts are just a few. More often than not, the presence of too much moisture is the reason why fungal disease takes hold. You can reduce the odds of fungal disease occurring in your garden by spacing plants out properly, pruning for good airflow, and keeping leaves dry. This means watering from below, rather than from above. Soaker hoses and furrow irrigation are better choices when fungi are present. (And they are always present.)
When fungal diseases strike, be sure to dispose of infected plant material in the trash, and sanitize garden tools between each cut.
I hope you now share my new-found respect for these amazing life forms.
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