Nick Maclaren wrote:
It isn't a single fungus, but a common ecological mode of many
fungi. It is believed that, just as most woody plants can grow
with or without mycorrhiza, some mycorrhizal fungi can grow in
other modes.
Your last sentence is correct, and is why many plants rely on
mycorrhiza in poor soils, but not in rich ones.

Understood. To go back to the first post, do you think it is wise to
let it out commercially, in that case to someone who just want to grow
better roses? It reminds me of the increasingly depletion of our peat
bogs and the unsustainability of it.