Here are a few questions I have I wasn’t able to find answers to online. I also reached out to the local mycological society but I think I’ve dipped too deep in the well…
How do mycorrhizal fungi and their hosts identify each other?
From Wikipedia: “about 80% of land plants species rely on mycorrhizal relationships with fungi to provide them with inorganic compounds and trace elements.” What do the other 20% that don’t rely on those relationships have in common?
Do gymnosperms have mycorrhizal relationships?
Out of the plants that have mycorrhizal relationships, are those exchanges necessary for survival for the plants and fungi or do they simply enhance each organism’s ability to access what it needs? (Edit: I think I can answer this myself at least partially. Some mushrooms definitely depend on certain trees)
I have become very interested in nature since Covid, and as I learn more, I have more/deeper questions (I’m self-taught and have experience tutoring AP Biology, but I’m not in the field professionally). I’m especially interested in connecting dots and understanding interrelatedness and evolution, among other things.
I know the answer to one of your questions,
3. Do gymnosperms have mycorrhizal relationships?
Yes they do. When I worked for Queensland forestry years ago we were growing “yellow pines” from the southern US and the Caribbean. We found we had to collect leaf litter from Mississippi forests to get the right mycorrhiza. Unfortunately introduced some pathogens as well
Q 4: Mycorrhizae aren’t always necessary. For example, ploughing destroys the mycorrhizae but we can grow crops in ploughed fields. But we have to drench the soil in fertiliser to make up for the lack of mycorrhizae.
It has been shown (I think for bird’s-foot trefoil Lotus corniculatus and common blue butterfly Polyommatus icarus) that some herbivorous invertebrates can’t complete their life cycle on food plants that lack mycorrhizae.
Plants exude chemicals into the ground. Mycorrhizal fungi search for this chemicals and enter the host plant.
These chemicals are exuded for many different reasons (allelopathy, communication w/ other plants, making the soil more suitable for extraction of nutrients etc.), but in most group the relationship is deep enough that plants make these chemical specifically to attract the fungi. In some plant groups the relationship is deep enough that the embryo in the seed is innoculated, so the plant is never without its fungus.
mostly that they grow in places fungi do not. One of the most prominent plant groups without mycorrhizae are Brassicaceae, which mostly grow in hevaily disturbed habitats with initial soils (gravel bars, rock crevicess etc.), where fungi are rarer, and more stressed about life. In such environments, the fungi would take more than they would provide, so the plant has no incetive to enter mycorrhizae.
OR alternatively, they grow in places where there is no benefit from having a fungus attached to you. benefits of mycorrhiza for the plants is increased availability of water and nutrients, in places where those are abundant and the competition is low, there is also no point.
Yes. not only them, but also ferns, lycopods, liverworts and mosses. Mycorrhiza is something that has been happening since before the plants had roots.
depends on the fungus and the plants. For some, the the relatioship is necessary (Orchids cannot complete their life cycle without a fungus, although many adult orchids are capable of living without one (and in fact are then fungus parasites, as the fungus enables them to germinate, but when they become photosynthetic, they sever the connection, giving nothing back to the fungus). Many Ericaceae have obligate mycorhhiza where both parters need eachother - that is why they are capable of colonising the extreme habitats, such as bogs and heaths)
Some mycorhizal fungi can also live without a plant, many cannot.
Some relationships are very specific (a species of plant and a species of fungi), some are not (a fungus can host many plant species, and a single plant species enter mycorrhiza with multiple fungi).
So the mycorhhiza can be obligate (necessary) or facultative (optional) for one or both of the partners.
Bonus fact:
Many pararsitic plant are actually not direct parasites on other plants, but actually parasitise fungi ( all parasitic orchids and all parasitic ericoideae), which in turn have to take more nutrients from their symbiotic parter to support the parasite.
(although for some of those relatioships, there is a possibility that the non-photosynthetic plant does provide some sort of service to the fungus and the trees around, possibly by reducing pressure from herbivores/fungivores through multiple possible routes).
I recently observed a mushroom that appears to be Suillus and a pine cone within a few meters of each other. They are both at home, so I obscured the locations, which means anyone else sees them several kilometers away from each other. Some species of Suillus associate with particular species of pine. Should I link the observations so that identifiers can look at the pine and identify the mushroom or vice versa?
I think it would be better to just write into the notes of the Suillus observation what tree species you found nearby, generally good practice for mycorrhizal mushroom observations :)
I can add to this that a lot of non-mycorrhizal plants have specific strategies to acquire nutrients without relying on fungi, e.g. carnivorous plants or cluster roots in Proteaceae. This relatively recent scientific review is a quite comprehensive summary of this and many other questions related to mycorrhizal fungi and their host plants.
Thank you and @ljazz for your thoughts on #2. I assumed plants that did not associate with fungi had special adaptations to be self sufficient, but it sounds like several factors, including lack of competitors in an environment and availability of nutrients, allow some species to thrive on their own.
And I have been fascinated by mycoheterotrophy too. And the fact that symbiosis and parasitism occur every way imaginable across and within kingdoms.
no, that is a different type of relationship;
in mycorrhiza, the plants are the leading partner, in lichen, the fungi are, the relationship is deeper and the mechanisms of connection is not the same.
a bit more to #2: Most species of plants can survive without mycorrhizae. In some, this is noticeable, they grow mcuh better with them as without, but most plants are self sufficient (hence why we are able to grow many of the plants in gardens, far away from their habitats and fungal parters).
For most species of plants, this relatioship is facultative. But there are groups of fungi, like most Glomeromycetes, which are the only ones that enter the most common form of MR, that are almost all dependent on plants., although plenty of other groups of MR fungi are facultative.
It is just less efficient to do things by yourself, if fungi are better at that.
Okay, I was wondering about house
plants and assumed they were like brassicas and didn’t need fungi, but this makes sense.
(Side question: how about air plants?)
I’ve also been thinking about @jhbratton 's comment about invertebrates not thriving on host plants that grow without access to their fungal partners. It’s interesting that the plant can thrive, but that the nutrient deficiency would be significant to the invertebrates that depend on it.
How does all of this come into play with invasive plants? Are they species that don’t require fungal partners or are they extremely broad in the number of fungal species they can partner with?