Mycorrhizal fungi: important for soil functioning and soil persistence?

As readers of this newsletter might know, I have been interested in operationalizing soil persistence (the capacity of a soil to be persist through time), and there is a previous newsletter about this (and with a bit of luck, soon a paper).

When we mentally go through our list of soil biodiversity, it is easy to find organism groups and taxa that we would list under “important for soil functioning”. Basically, you would find examples from bacteria, archaea, viruses, fungi, protists, nematodes, microarthropods, earthworms and so on. They will be contributing in some way to various important ecosystem process rates, such as nutrient cycling, soil carbon storage, primary production, etc.

But how long is our list for groups of organisms that we would highlight under making soil persist as well, so in addition to being functionally important for a major ecosystem process rate?

Maybe that list is a lot shorter. A lot of organisms will be involved in decomposition, but you could make the case that this leads also to a decrease in organic matter (in addition to nutrient mineralization), including organic matter that serves as binding agents for soil aggregation. Less binding agent means less stable soil aggregates. This is the “loss” side of soil persistence, and what about the “gain” side: so making new soil. Who would you list there? Sure, a bunch of fungi and bacteria that help with transformation/ weathering of minerals and with colonization of new materials that become soil. But are they necessarily on your list for major ecosystem process rates?

Root-colonizing microbes are maybe good candidates for being good for general soil functions and for persistence, because they sit at a critical biogeochemical interface, but can we make a solid argument how N-fixing bacteria are important for soil persistence? Or other bacterial symbioses with roots? They certainly are super important for primary production, but are they also for soil persistence?

Ok, then how about root symbioses with fungi then: they are definitely important for ecosystem process rates, at the very least primary production. But the extraradical hyphae (among other things) of mycorrhizal fungi are important for stabilization of soil aggregates, making a major contribution to persistence of soil. We know this mostly for mycorrhizal fungi, to be honest, and not so much for other root-symbiotic fungi. It is entirely possible that other root symbiotic fungi have that same effect on soil stability, we just don’t know that much about it. We don’t know this yet for some groups of mycorrhizal fungi either, take Mucoromycotina fine root endophytes, for example. Most work by far has been done on arbuscular mycorrhizal fungi (and not so much ectomycorrhizal or ericoid mycorrhizal fungi).

So, in other words, given what we know right now, who comes close to (arbuscular) mycorrhizal fungi in terms of being important for a major ecosystem process and for soil persistence? Am I overlooking something? I admit I am a bit biased…
Please let me know in the comments! :)