im reading a lot of research about the mycorrhizal network because this is a HUGE emerging area of research and there is so much new stuff coming out its sooooo neat
So basically "the mycorrhizal network is how trees send each other nutrients and help each other" is wrong,
but the main reason people were mad at it—because they thought everything in the ecosystem is selfish and competitive acting for its own interests—is much wronger.
How come?
Well...fungi aren't just a postal service for trees. They have lives of their own! Plants aren't just controlling the mycorrhizal network to send nutrients where they want, they are communicating with the fungus and negotiating the terms of that relationship.
The genetic basis in plants for forming the mycorrhizal symbiosis is old. REALLY old. Like, "before plants even came onto land" OLD. Other forms of symbiosis, like what legumes have going on with the Rhizobia, are using the same genes to do their thing. There's a LOT of genes involved with creating the symbiosis, including some redundancies just to be safe, and we're only just now starting to understand them.
Why so many genes? What are all these genes for? Everything! Communication chemicals, hormones the other partner will respond to, flipping switches in the other partner's genes. There was a lot of arguing over which partner, the plant or the fungus, was "controlling" the partnership, but this question turned out to be total nonsense. Both symbionts have to recognize each other, respond to each other, prepare for symbiosis by adjusting how their genes are expressed, form the symbiosis, and continuously negotiate the relationship by exchanging chemical signals. Both can actively select the partner that offers the best benefits. There's even experiments where it's been shown that if the fungus turns parasitic, the plant will start secreting fungicidal chemicals. (But also the mutualist fungi in the experiment outcompeted the parasitic one when the pots were seeded with both.)
Mycorrhizal symbiosis is an incredibly intimate relationship. Like, the fungus produces special organs that literally grow inside the plant's cells, and the plant is actively participating in allowing this to happen. The plants and fungi have genes for hormones used by the other species, they have soooooo much stuff encoded in their DNA for interacting with their symbionts, it's like, blurring the lines for whether they're even separate organisms. There are SO many chemicals involved in communication between them and we only understand a few of those chemicals.
This is SO MUCH COOLER than if the plants were just using the fungus as a passive conduit to communicate with and support each other. The fungus is actively participating!
We were fools and assumed there had to be one partner that was "in control," but both plant AND fungus have to initiate and to some extent they're each engaging on their own terms! Or maybe it's better to think of them as one and the same organism?
We're also finding out that there's a lot more types of mycorrhizal symbiosis than we thought (at least five) and a lot more variety in how it works.
And that's not even getting into fungal endosymbionts—fungi that live inside plant cells completely instead of having part of them be outside and in the soil. They aren't considered mycorrhizae because they're fully inside the plant cells and not connected with any soil fungi network but they do a lot of complicated things we don't understand and interact with the plant's other symbionts.
Fungal endosymbionts produce a lot of chemicals that are useful to the plants in some way, and it turns out, that a lot of them kill cancer. Seriously, we've gotten a LOT of anti-cancer drugs from these guys. I think it's because they have to bypass the plant's immune system, but they also fight each other/other little guys that get inside plant cells, so they kind of...are part of the plant's immune system?
And what's MORE
Is that plants and fungus aren't the only things part of this system! There's also bacteria that are symbiotic with the plants and fungi! Even the endosymbiont fungi have bacteria that are endosymbionts inside THEM. Double endosymbiosis.
I think I read one paper saying the bacteria use the fungi to get around? Like that's how Rhizobia find their way to the legume roots in the first place? Have to double check that one