Orchids and Fungus Student Reading

If you’ve ever eaten bread or mushrooms then you have eaten fungus. The plural of fungus is fungi, and fungi are not animals or plants, they’re something different. Fungus is an important part of life for people and it is just as important for plants. But what is fungus?

Mushrooms growing in leaf litter. Stu's Images, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17469163

There are two types of fungi. Some fungi, like the yeast that we use to make bread, are uni-cellular, made of one cell. Some fungi are multi-cellular, made of many cells, like the mushrooms people eat.

Unlike plants, that make their food from the sun through photosynthesis, fungi can’t make their own food. Fungi are heterotrophs. They absorb, or take up, the nutrients from the environment where they live.

PARTS OF A FUNGUS Let’s look at the parts of the most common type of fungus you might see, bread mold. The body of the fungus you see growing on your bread is called the mycelium (my-seal-E-um). The bread mold decomposes the bread around it for nutrients.

Different types of mold growing on bread. https://pixabay.com/en/age-bacteria-bio-biology-bread-1238290/

If you were to look at the mycelium of the bread mold under a microscope you would see a dense mat of thread-like hairs all laying on top of each other. These hair-like things are called hyphae (high-fee). The hyphae are like the roots of a plant that has no stems or leaves, but remember fungus is not a plant.

Instead of just sucking up water and nutrients like plant roots do, the hyphae secrete or ooze enzymes and chemicals. These chemicals decompose or break down stuff in their environment so that the hyphae can soak up the nutrients of the bread as it breaks down.

Black bread mold hyphae. https://commons.wikimedia.org/wiki/File:Rhizopus_stolonifer4.JPG

Another very common fungus you might see, or even eat, are mushrooms. Mushrooms grow from the hyphae of fungus. When you turn over a rotting log or dig in soils and see white looking threads, these are most likely fungal hyphae.

Fungal hyphae https://commons.wikimedia.org/wiki/File:Hyphae.JPG

These hyphae often make mushrooms. Remember, fungi aren’t plants but they have a lot of similar parts. The mushrooms are like the fruits of the plant. They make spores, which are like seeds. The spores grow into new fungal hyphae. Not all hyphae or fungi make mushrooms though.

FUNGUS FRIENDS Fungi are pretty good at getting nutrients from the soil and where they live. But, some fungi just cannot get enough by themselves, so they team up with plants. This is called symbiosis (sim-by-Oh-sis), when two different living things live closely together. Often symbiosis is beneficial for both of the things that live together, like fungi and plants, but not always. Sometimes one organism may benefit more than the other. Sometimes neither organism benefits and they just live together.

The word mycorrhiza (my-core-eyes-ah) is Latin for “fungus-root.” This is when fungi lives inside the roots of a plant. Almost 90% of all plants on earth have mychorrizal fungus in their roots. The fungus inside the plant roots helps break down the soil or nutrients around the plant. This frees up minerals and nutrients which is good for the plant. The plant makes food for itself through its leaves and photosynthesis. It shares this food with the fungus in its roots.

Mycorrhizal fungus, stained red, in plant root cross section. https://www.flickr.com/photos/occbio/5581642190

ORCHIDS AND FUNGUS Orchids are one of the biggest flowering plant families on earth, and they too need fungus to live. Orchid seeds are tiny, and like dust. When they land on the ground they don’t have any food to help them grow, like apples or acorns do. Instead, they act as hosts or homes to fungus. This fungus breaks down nutrients in the soil and helps the tiny seeds grow into tiny root-like tubes called protocorms (pro-toe-cor-ms). The protocorms eventually grow leaves and turn into orchid plants. But, some orchids never grow leaves and they depend on their mycorrhizal fungi for food.

Orchid seeds, like these, need fungus to grow into plants.

All orchids need their root-fungus to survive, even if they have leaves. Unlike most symbiotic relationships in plants, the orchid-fungus relationship is not thought to be entirely beneficial. It’s not clear what the fungus gets from living inside the orchids.

ORCHIDS AS SIGNS One reason Smithsonian scientists study orchids is because all orchids need fungi to grow. If the fungi in a forest or community is out of balance or missing then the orchids that live there may not grow or survive. This means that orchids can be bio-indicators of the health of the soil and environment. The presence, absence, and health of orchids can tell scientists a great deal about what is going on in the environment.

Downy Rattlesnake-plantain (Goodyera pubescens) https://www.flickr.com/photos/59898141@N06/11449091464

Reading Questions

1. How do fungi get the food they need to live? 2. What is symbiosis? 3. How does a fungus benefit from being symbiotic with a plant? 4. How does a plant benefit from being symbiotic with a fungus in its roots? 5. The reading suggests that orchids are good bioindicators. Explain why in your own words.