Mushroom Madness: Part 2 Life of a Fungi
Welcome back to Fun with Fungi! A four (or more?...!) -part series on fungi and mushroom cultivation. In today’s installment, we’ll explore the fungal life cycle and some of the roles that they play in a healthy ecology. But first, a joke!
What did one spore say to its grandmother?
Hi gamete, I’m so haploid to see you!
Get it!? No? That’s okay! By the time you finish reading this it’ll make total sense 😁
Okay first, what the heck even are fungi? They are not animals, nor are they plants; they are their own Kingdom entirely! Fungal cells are made of different materials and their growth and reproductive habits are different from both plants and animals, however fungi do appear to be more closely related to animals than plants [1]. In this article we will be primarily focusing on what are called “higher fungi” as they are more familiar to us land creatures, however the “lower fungi” -including many aquatic species and the awesome slime molds- are no less important or interesting and may be the subject of a future post. From here on, you can assume “higher fungi” when I say “fungi”. Of course, there are always exceptions and this will be a simplification.
While the mushroom is the most familiar part to many of us, the fungal organism is much more than just the mushroom. The majority of the organism exists as a network of cellular filaments called hyphae (singular hypha) that branch out through the soil, wood, or whatever the fungus happens to be growing on (the substrate). The collection of all these hyphae, the “body” of the fungus if you will, is called the mycelium (my-silly-um). Generally we don’t see the mycelium because it is underground or inside a log, but a little digging in the forest floor will often reveal an immense web of white, or sometimes orange, pink, or even blue mycelium weaving the earth beneath our feet together! The mushrooms we know and love are just the reproductive structures of the fungi.
“The majority of the organism exists as a network of cellular filaments called hyphae. The collection of all these hyphae, the “body” of the fungus if you will, is called the mycelium.”
As the mycelium grows, the hyphea produce a mixture of digestive enzymes and chemicals that it exudes out of itself. The release of these digestive enzymes breaks down the substrate material, decomposing plant material and minerals alike. Once broken down outside the body, the mycelium then uptakes all the available nutrients and shuttles them around its body as needed, and sometimes even between other organisms.
Droplets of yellow digestive enzymes secreted by the winecap fungus consuming this log.
In response to various stressors or environmental cues, the mycelium may decide that it’s time to reproduce. This could be because the fungus has fully colonized the available resources from a given location, say for instance, an entire section of a log, or it could be due to a strong rain storm or changes in temperature.
Flushes of various mushrooms. From left to right: Winecap (Stropharia rugoso-annulata), Common Oyster (Pleurotus ostreatus), False Turkey Tail (Stereum ostrea), Mica Cap (Coprinellus micaceus)
“The mushrooms that we know and love are the reproductive structures of the fungi!”
The mycelium will produce one, or often many more, mushrooms as a means of sexual reproduction. The gills on the underside of a mushroom (or pores or teeth, depending on species) produce the reproductive cells of fungi, called spores.
Spores are similar to sperm and egg cells in animals. In both animals and fungi, most cells in the body have two copies of their DNA; one from each parent. The reproductive cells (sperm, egg, spore), however, only have one copy of the DNA. These cells are called gametes, and contain some mixup of DNA from the two copies in the parent. Cells that only have one copy of DNA are called haploid, whereas the body cells with two copies are called diploid. When two compatible gametes meet, they fuse together and form a new diploid cell- the new organism is conceived!
Spores are interesting because they can actually grow before mating, unlike animal gametes. Spores that germinate can create haploid hyphae that reach out in search of a suitable mate. Once two suitable haploid hyphae meet they become diploid and create a new mycelium for a genetically distinct new fungus.
Ungerminated spores of the fungus Panaeolus cinctulus collected from local specimens and viewed under light-optical microcopy.
*For microscopy purposes only
As that fungus grows and develops, eventually it will encounter conditions that cause it to produce mushrooms, and the cycle starts again!
A note on spore compatibility: it is a bit more complicated than in animals. Whereas animals only have two mating types (sperm and egg), each of which is only compatible with the other, some fungi can have many more. The fungus Schizophyllum commune, for example, has a whopping 23,328 mating types! [2]
Now that we understand the lifecycle, let’s zoom out a bit and look at how fungi function in terms of a whole ecology.
As we’ve talked about before in our blog post on wood chips, fungi are critical in making nutrients available to other organisms, especially plants. Those digestive enzymes break down dead plant material and recycle it, and also convert inorganic minerals into forms that the plants can uptake and use. But the plants don’t have to wait for the fungus to die to get those nutrients, in many cases, the plants and fungi trade in real time while they are alive! These fungi that partner with plants are called mycorrhizae (my-co-rye-zuh).
Mycorrhizal fungi attach directly to the roots of the plants, sometimes even penetrating their cell walls to get unobstructed access to the cell! The fungus will provide the plants with nutrients, minerals, water, and even medicinal compounds that the plants can use to fight off infections. In exchange, the plant provides the fungus with sugars produced from photosynthesis.
But mycorrhizea are not confined to one fungus for one tree. Each plant can harbor multiple species of mycorrhizae, and each mycorrhizal fungus can connect thousands of trees and other plants! Together, they form a massive interconnected web sharing resources and information. Plants can send messages about pest and disease infestations through the mycorrhizal network, allowing other plants to prepare themselves and be ready. In the forest, trees will even send resources to trees of other species, because they know that the health of the forest as a whole is dependent on everyone being healthy. A lesson we humans could really stand to learn.
“In the forest, trees will even send resources to trees of other species, because they know that the health of the forest as a whole is dependent on everyone being healthy. A lesson we humans could really stand to learn.”
For those interested in doing a deeper dive into the science of mycorrhizae, told in a fun and accessible novel format, I would highly recommend the book “Finding the Mother Tree” by Suzanne Simard. But try not to buy it on Amaz*n if you can avoid it.
It is estimated that over 90% of all plant species form these mycorrhizal relationships, and many are absolutely dependent on them, and would be completely unable to survive without them. Combine that with the ability to remediate pollution and provide food and medicine, and you can see why it’s so important that we get as many species of fungi back into as many places as possible!
Next week, we’ll look at some ways to do just that! We’ll explore a few different methods for at-home and small-scale commercial mushroom cultivation, so make sure you’re subscribed because you don’t want to miss it!
For now, hopefully you learned something new about fungi, and if I did my job right, you should now find that joke at the beginning hilarious!
See you next week!
References
Wainright, Patricia O., et al. "Monophyletic origins of the metazoa: an evolutionary link with fungi." Science 260.5106 (1993): 340-342.
Kothe, Erika. "Mating types and pheromone recognition in the homobasidiomycete Schizophyllum commune." Fungal Genetics and Biology 27.2-3 (1999): 146-152.
