Mushrooms grow in substrate that varies in carbon/nitrogen (C/N) ratios and other factors depending on the species. These vary from hay to straw and compost, to other organic by-products and waste materials.
Mushrooms are able to balance the flux of material by consuming and releasing nutrients into the system, including plastics [41]. The mycelium also hydrates the substrate through aqueous secretions.
Substrate
Mushrooms grow from substrate, which is the medium for mycelium to thrive. Mushroom substrate is nutrient rich and can be made from a variety of things. Cardboard, for example, is a good mushroom substrate. It’s a recycled material and it’s also lignocellulose-rich. It’s a good choice because mushrooms thrive in that kind of environment. The mycelium grows all throughout the substrate and cannot be separated from it. When it’s fully colonized, the mycelium can be fruited, and mushrooms grow from that fully-colonized substrate.
When you’re growing mushrooms, you want to make sure that your substrate is sterilized to eliminate any microbial contaminants. There are many different ways to sterilize, including cold sterilization using chemicals, hot water scalding, hydrogen peroxide, and pasteurization in an autoclave. Once your substrate is sterilized, it’s ready for inoculation.
You’ll need to choose a fungus that’s suitable for your substrate and then get it ready for colonization. There are a few different ways to do this, but the most common way is to mix a small amount of spawn with a large amount of substrate and put it into a sterilization bag. The spores will then germinate and start to grow and expand in the bag.
Once the spores have grown and started to spread in the substrate, they will take up more and more nutrients. This will encourage the mycelium to grow out into the substrate and become thicker and more robust. Depending on the type of fungus, the mycelium may choose to grow in an exploitative fashion, forming a dense, branchless network, or it may choose to follow the shortest path of resistance, resulting in thin hyphal networks that are more spread out.
The process of colonization can be accelerated by mixing in other ingredients with the spawn. For example, some people like to add a little rye grain or straw to their substrate mixture to make it more nutritious and allow the mycelium to grow faster. Other ingredients that are often used include wheat bran, psyllium husks, and other organic materials. The idea is to get the mycelium to grow out into the whole substrate so that it’s a fully-colonized substrate.
Hyphae
Fungi are eukaryotic organisms that appeared on land more than 450 million years ago. Like plants they are heterotrophs, but they lack chloroplasts for photosynthesis and must obtain all of their food from external sources rather than through internal synthesis of carbon dioxide and water. In order to get the most nutrition out of their food, fungi secrete exoenzymes that break down complex organic molecules into smaller ones. This process is called digestion, and the nutrients are then absorbed into the mycelium of the fungus. The fungus stores the digested polysaccharides in its cells as glycogen, which provides energy for growth and other essential processes.
The fungal mycelium consists of microscopic filaments, or hyphae, that branch repeatedly into a complicated, radially expanding network, known as the thallus of the typical fungal species. The hyphae that make up the mycelium have a thick cell wall, called chitin. The mycelium varies from one fungus to the next, depending on its function and needs. Some fungi produce a fruiting body, such as the mushroom shown in Figure 2.3.2.8, by sexual reproduction with a basidium that produces four sexual spores. Other fungi, such as the yeasts, reproduce asexually by budding.
Once a spore germinates it grows from the tip of a hypha and branches out evenly in all directions. As the hyphae grow they produce cross-connections, which allow nutrients to quickly move throughout the mycelium. These connections may have walls, called septa, which separate the hyphae into individual sections or cells. Fungi with septate hyphae are called coenocytic, while fungi with no walls or cell membranes between the hyphae are called nonseptate.
Some fungi develop a special nuclear condition that enables them to conserve scarce materials such as nitrogen. They do this by forming special cellular structures called clamp connections during septa formation. These connections help to conserve nutrient molecules and place them near the active growing tip of the hypha, where they can be used more quickly for enzyme production or cell wall synthesis. This is a common feature of many basidiomycota and is what allows the mushrooms to grow so rapidly.
Nutrients
Fungi belong to a kingdom of their own, separate from plants and animals. Unlike plants, which grow their own food through photosynthesis, fungi consume nutrients from outside sources. They enter their food sources through their mycelium, secrete enzymes that digest the food inside them and absorb the resulting nutrients. Fungi are essentially the recyclers of nature, consuming dead trees and rotting logs or animal dung and returning the nutrients back into the soil to help other plants grow.
Mushrooms grow by a process called spore germination, whereby spores (which are the fungi’s seeds) are released from a sporophore — an umbrella-shaped structure located at the tip of the mushroom stem. The spores are dispersed into an extensive network of threadlike strands, called mycelium, which is the primary growth medium for mushrooms.
In order to get started, mycelium requires a substrate that is moist and full of nutrients. Unfortunately, this type of environment is also ideal for bacteria and mold to grow. If left unchecked, these contaminants can quickly outperform mushroom mycelium and take over the substrate before mushrooms can colonize it. Therefore, to ensure that mushrooms thrive, it is necessary to supplement the substrate with nutrients at casing time.
A number of different types of nutrient supplements are available for growing mushrooms, including fish flakes, blood meal, kelp, poultry manure and compost. The choice of nutrient depends on the type of spawn being used and the desired end result. Supplementing at casing can increase yields by up to 100%, but this is only possible if all pathogens and weed molds have been eradicated from the compost or substrate before the spawn is added.
Another important factor in a healthy mushroom crop is the proper temperature. The optimal temperature for spawning is between 70 and 80 degrees Fahrenheit. Failing to provide the correct temperature can result in poor fruiting, a deteriorating mycelium and a reduced rate of spore germination.
A number of studies have shown that nutrient supplementation at casing can improve mushroom quality. It can also increase the rate at which a mushroom grows. Some research suggests that the rate of growth is proportional to the amount of nutrient that is added, while other studies indicate that the amount of supplemental nutrient does not affect the final yield or quality of the mushroom.
Temperature
Mushrooms grow from tiny, threadlike spores that are too small to see with the naked eye. The spores are mixed with sawdust, straw, or wood chips for nutrient support, and the blend is called spawn. The spawn acts like a starter for bread; it grows for a while before anything resembling a mushroom pushes its way through the surface of the substrate.
Different strains of mushrooms prefer different temperature ranges, a function of where they originally grew in nature. Some can be acclimated to new climates over time, but the simplest way for home growers to ensure optimal growth conditions is to use a spawn bag that contains mycelium adapted to their local environment.
The spawn grows on the substrate, which is sterilized in preparation for the spawn’s arrival. The mycelium absorbs the nutrients of the spawn bag and uses its own enzymes to stimulate hyphal growth on the substrate. After a period of several weeks, the mycelium forms fruiting bodies and is ready to be harvested.
If the spawn is exposed to temperatures too low, it will cease to grow and may die. The mycelium requires warmth for survival, and it is a critical factor in ensuring proper nutrient transfer to the fruiting bodies.
Extremely high temperatures cause mycelial growth to slow down, and they often produce acid-forming bacteria that can degrade the substrate, reducing its nutrient availability [78].
In addition, excessive heat can cause a mushroom to release toxins into the air. These toxins can damage the growing substrate and harm surrounding plants, and they may also encourage unwanted microorganisms to proliferate.
Mushrooms can be a natural alternative to plastic packaging materials, and research is underway to develop materials that are more environmentally friendly than traditional plastics. For instance, the mycelial biomass of Sclerotium rolfsiiis can bio-weld and mold materials together, as well as break down plastics (Modanloo, Ghazvinian, Matini, & Saporta, 2021; Da Luz, Dos Santos, Kasuya, & Clark, 2020). The mycelial mass also has the ability to absorb heavy metals such as cadmium and radioactive isotopes from contaminated soil and water (Kasuya et al., 2016).
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