For millions of years, plants and fungi have had complex and intricate marriages with each other, resulting truly in a soap opera for the ages! There’s love, lust, friendship, and even enemies between plants and fungi. In love, they work together and benefit each other. In lust, one takes advantage of the other, then loves them. In friendship, one helps the other without any expectations. In enemies, they fight each other. Now that I’ve tortured you with my poor metaphors, onwards to the actual content!
For the most part, plants and fungi actually benefit one another. In the most common relationship, the plants provide the sugars and energy, and the fungi harvest the nutrients and trace minerals that the plants need. This is a mutualistic relationship, which is symbiotic. Trading one good for another. It’s rather beautiful, and benefits both organisms BUT (and this is the darker side that they don’t tell you) that means that they are dependent on one another.
Sometimes, the relationships are detrimental. That’s when DIFFERENT SPECIES of fungi attack your plants and cause foliar blight, root rot, and other plant problems. Usually this is because something is too wet somewhere for too long and the pathogen is present. That can be fixed by… you know… not getting your leaves wet, and waiting until your soil is dry before watering. (lol)! This reminds me of the disease triangle for plants (pathogen, host, and conditions have to be right for disease to occur). I’ll spare you that lecture, because it can get complicated. In any case, you can’t go wrong with airflow, heat, and light.
Other relationships are complicated. Some are commensal, meaning that one organism gets a benefit, and nothing happens to the other – no benefit or detriment. Still more, in the world of orchids and the world of endophytes, relationships get pretty sticky. All plants have endophytes, and some endophytes have opportunistic personalities – they work with the plant when times are good, but turn on the plant when times are rough. Even more interesting is the fact that orchid seeds parasitize a fungus in order to germinate, making orchids parasites until they can photosynthesize and just absorb that fungus as a lifelong endophyte. Nature is really metal sometimes.
Scientists agree that fungi colonized land well before plants did. As to when they colonized land is a difficult question to answer, as our approximations are based on fossil records, which only record anything with hard body parts that can be fossilized… Most fungi are super soft, so we have to guess based on genetic markers and good ol’ fashioned logic, based on common synapomorphies of all fungi as to when they came onto land. Regardless of when fungi colonized land, we know that they added a component to soils that was not present in soils before – large amounts of carbon and free minerals. Fungi also play an immense role in water retention. The filaments of fungi may have served as proto-roots in primitive plants (roots evolved way later actually). Without a way to survive desiccation, life on land would not exist. Fungi helped to not only break down the rocks on land, but also to help retain water on land, and consequently help pave the way for plants.
It’s my own conjecture that this process started with things at the waterfronts that wash up on shores. Things flop on land or get tossed onto land during a storm, and consequently rots. This breaks down and mixes with the earth directly underneath it. This creates a buffer layer for things to get interesting, and the ground to not dry immediately. Suddenly, other organisms with a semi-dry tolerance get washed ashore during low tide, and survive long enough for high tide to rehydrate them. By organisms, I’m talking about kelp and other macro algae. Over time, the proto-plant organisms with the highest dry-tolerance make friends with fungi to keep them hydrated between the tides, and the rest is evolutionary history.
Lichens: an ancient oddity
Of the little things that we do know, one of the first and oldest interactions between plants and fungi is the symbiotic relationship known as a lichen. A lichen is formed from cells of algae and a filamentous fungus weaving together to form a unit that is different from either organism. The algae feeds the fungus sugars and the fungus helps to retain moisture and occasionally provide nutrients from either the substrate that they’re growing on or from dust in the air (sound familiar?).
On the surface, this relationship seems symbiotic, which would mean both organisms can exist separately, but cooperation makes survival easier for both organisms, kind of like cohabitating with roomates. However, this is not the case for the lichen. While the algae can live without the lichen fungus, the lichen fungus cannot exist alone. It appears to have lost the ability to fend for itself over the eons.
Other fungi in the soil that we know that interact with plants belong to three major groups: the Basidiomycetes, the Ascomycetes, and the Oomycetes. Most endophytic fungi – that is, fungi that lives between living plant cells – are Ascomycetes, with some being Basidiomycetes. And the relationships of many endophytes to their plants are symbiotic. (Ectophytes exist too, but it’s too lengthy for me to type right now).
Plants do complex chemistry to make all the aromas and flavors that we know and love. Interestingly enough, endophytes (and yeast) are largely responsible for the flavors in wine! In fact, the same variety of grapes will not taste the same unless they have the same/similar endophyte species within them. That’s a part of the reason why, given roughly the same climate and conditions with a cultivar of grapes, you will get very different results.
Mushrooms in my soil?!
Occasionally, the fungi which live in the soil or the endophyte (or in some cases, it is the same fungus) may be in ideal conditions, and will reproduce sexually by producing a mushroom. This is perfectly normal, and is even considered to be good luck in some areas of the world. So no, mushrooms aren’t bad! (side rant – I can’t stand when people complain that other organisms sometimes live with plants. Like nature is interwoven! Things live together in communities! If it isn’t doing any damage, a mushroom friend is fine. On the flip side, it may mean that your soil is staying too wet for too long. You may want to increase dryness).
We tend to think of houseplants as just the plant, but we often forget that each pot of soil is a tiny ecosystem. Microbes like bacteria and fungi live in the soil and some of them are helpful to our houseplants, while others are harmful. Most fungi in healthy soil exist to help the plant, and do so by many means.
To communicate with the plant, the fungus must connect with its roots. Through these root connections, the fungus can send and receive chemical signals to and from the plant. Some fungi will stay outside of the roots (ectophytes), while others may penetrate and extend into the root cells (endophytes).
Regardless of which type of fungus the plant is interacting with, the fungus accomplishes two major functions:
First – the fungus lowers the pH of the soil by selectively absorbing NH4+ (ammonium) and kicking out the H+. This helps solubilize and mobilize metals and phosphates that are essential for your plant. As a consequence of the ammonium absorption, this excess source of nitrogen also leaks into the plant through the fungal-plant junctions. The plant trades carbon in the form of hexoses (sugars) to the fungus for nitrogenous compounds, phosphates, and other minerals.
Second – not only do fungi provide nutrients to the plant, but they also allow chemical communication amongst plants. This network of fungi has been shown to allow insect-attacked plants communication to their neighbors. It has been measured that nearby plants will boost their own innate defenses if they hear over the mycelium that one of their neighbors is being attacked – sort of like your emergency contact. Some plants use the mycelial network for more devious purposes – spreading toxins and growth suppressants so that other plants cannot grow. Others use it for more altruistic purposes like sharing sugars and nutrients to neighboring plants.
So, we know that the relationship between plants and fungi is important, and that the key to plant success is allowing them to work together. In many outdoor gardens, it’s recommended to increase the types of fungi in the soil by buying inoculum and inoculating the soil. In your houseplants, you don’t HAVE to do that, but it does help (though indoors, the growth rate is so slow that it really doesn’t matter, but I add the inoculum anyway to most of my plants because I like seeing mushrooms pop up lol).
In the case of brown leaves on your plants, it’s most likely just a fungus that is invading because the leaves are too moist, or you keep spritzing those plants that don’t need to be spritzed (I’m looking at you, Fiddle Leaf Fig). Occasionally, the fungus is crafty enough to invade without moisture, or may be a dormant endophyte that’s an opportunist. Those endophytes work with the plant when times are good, but when conditions get unfavorable, the fungus will turn on the plant and start digesting it! This is not THAT common, but does happen.
Have any questions about plant fungi or mushrooms in your soil? You should message me @botanictonic on instagram or firstname.lastname@example.org ! If you like what I am writing, please leave me a tip on Venmo! @C-Sat (if it asks for a number, it’s 9898)