The Daily Bucket: Fungi and Mycelium: Fun, Fine Dining and Life Itself

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Hyphae and Mycelium:

 Many fungi including mushrooms, are composed of assemblies of cells like many other life forms. (Exceptions include the yeasts which are single cell fungi.) In their simplest form these fungal cells form microscopic tubules called “hyphae” (Greek for network).  Hyphae are what grow from germinated fungal spores into tubular structures.  As they grow throughout the soil or other substrates, (roots, tree bark, dead plant matter)  they form interconnected branching networks of cells that are called “mycelium.” The mycelium is essentially a feeding net that conducts nutrients and water to and/or from other plant material much like plant roots do.

The hyphae at the ends of the mycelium secrete enzymes that break down organic matter into digestible units that supply the network with nutrients. Along with bacteria,  they decompose the dead and dying plant materials that make up the forest floor. The mycelium and its mushroom shown in the lead photo are decomposing the stump to become nutrients of the forest floor and available to sustain other life forms. Without these fungi, our forests would be piled high with undecayed logs and debris. 

These mycelial structures are found nearly everywhere in soils and organic matter. When environmental conditions are right for a particular mycelium, such as after a rainy period, it will send fibers above ground and form what is called a “fruiting body” or the mushroom that we see on the ground, trees, and elsewhere. It is these fruiting bodies that form and disperse their fungal spores for future generations. The mycelial networks then provide the mushroom with its nutrients. In most woods and fields the ground is interlaced with these networks. Although we rarely see it, mycelium is under our feet especially in the forest where they interact with trees.  These forest networks are often referred to as the “Wood Wide Web.”

Taxonomically, fungi are classified as one of several kingdoms of life along with animals, plants and some other organisms. (Just how many kingdoms there are is still a matter of debate. See The Tangled Tree for history and debate.) Although we often think of fungi as plant-like as they grow in the ground and on trees among many other places, they are in fact considered more closely related to the animal kingdom than to the plant kingdom, having diverged/evolved from the animal kingdom more recently than did plants.  

There are several phyla of fungi but here I will mostly address two that includes those we call mushrooms. These two phyla differ in how their reproductive spores are formed and stored. Taken together these two phyla, “Basidiomycota” and “Ascomycota,” now constitute a sub-kingdom of their own called Dykarya and are often referred to as “higher fungi.” 

The Basidiomycota includes those we typically think of as mushrooms having a stem (stipe) and cap. Under the cap are either gills or pores where their reproductive spores are formed and stored in club-like structures called basidia until released. Common examples include puffballs, fairy rings, polypores (brackets or conks), boletes, chanterelles, earth stars, jelly fungi, rusts and some yeasts.

Below are several fungi from this phylum with very different external characteristics although all store spores in basidia. 

The second Phylum, Ascomycota is also called “sac” fungi as their pores are held internally in sacs. Popular culinary examples include morels and truffles, along with bakers and brewers yeasts. Also a sac fungus is penicillium that forms the rind on cheeses such as Brie as well as for antibiotics.  A couple of other sac fungi are shown below.

Symbiotic relationships between Fungi and Plants

Although fungi and plants are from separate kingdoms of life, the two often live in intimate relationships or symbiosis. If both the plant and fungus benefit from this relationship it is called Mutualistic.  Lichen as a composition of algae and fungi is a prime example of mutualism.

One of the more important examples of mutualism describes relationship between fungal assemblages that run in networks through the soil and connect with trees and other plants.  In these fungal – plant relationships the two organisms provide nutrients that the other can’t get enough of or can’t get at all on their own.

In mutualistic relationships, the two (or more) organisms provide one another with essential or growth promoting nutrients. Since fungi do not photosynthesize, they rely on plants to provide them with sugars for example that they need for energy.  These nutrients are conveyed to fungi through the mycelia networks that join up with plant roots. Mycelia that joins up with tree or other plant roots are called Mycorrhizae (fungus root).  Some mycorrhizae connect externally with the plant root enshrouding it to transfer and receive nutrients. These “ectomycorrhizae”  interact with a limited number of trees which include fir, pine, birch, alder and oak. This is the type of mycorrhizae that produces the fruiting bodies we call mushrooms. Other mycorrhizae actually infiltrate into the root cell structure for more direct transfer of nutrients.

Plants also obtain a number of minerals and nutrients from the fungi in these relationships including phosphorous, nitrogen and water. During drought conditions, a tree root systems might not be extensive enough to supply sufficient water for the tree to thrive. The mycelia networks are much more wide reaching than tree roots and can often access water to supplement the trees’ water supply.

These relationships are fascinating and the subject of considerable research today. It has become clear that fungi and many plants are mutually dependent on one another. One scientist who studies these relationships has suggested that upwards of 90% of all plant species depend on this form of mutualism. 

Truffles and trees

The highly sought after fungus, the truffle (genus Tuber among others) also has an intimate mutualistic relationship with tree roots. In fact, truffles can’t live without trees although they share many nutrients extracted from the soil through the mycorrhizal connections with the trees and in turn receive carbohydrates to promote their own growth.

Truffles, like mushrooms consist of underground mycelia networks. At certain times (often summer and fall) they develop their fruiting body that we know as the truffle (lump). Unlike most mushrooms, the fruiting body grows totally underground from just below leaf litter ( ~1”) to a foot or so into the soil.

The fact that truffles replicate by spores presents a reproductive problem. Being underground there is no breeze to waft the spores off to a new site to germinate and develop. The solution to this problem is that they develop a strong aroma that can be detected above ground by olfactory sensitive animals. The aroma which has been described as a “dirty socks” odor is enticing to forest animals that would dig them up. After eating them and on defecation, the animal “plants” the new truffle spores in the ground to start a new cycle. Historically pigs were used in Europe but now they use specially trained dogs.

As certain truffles bring in astronomical prices, being the most expense food substance in the world (often many thousands of dollars per pound,) many farmers have tried to grow them commercially with only partial success. It is difficult to duplicate Mother Nature.

The video below illustrates these processes.