I have been experimenting in recent years with inoculating all my tree seedlings with edible
Mycorrhizal species of fungi. I haven't yet found a complete list of edible
Mycorrhizal fungi but some have been identified and I have used Penny bun (Boletus edulis, most Boletus are mycorrhizal) which I have purchased in supermarkets.
Also Wood Blewit (Lepista nuda), Chanterelle (Cantharellus cibarius) and some Boletus that I picked wild. What I normally do is to mash up the fungi with my potting soil and then plant up my seedlings into this. I have also just left pieces of broken fungi on the top of the soil so that the spores naturally disperse into the pot soil. All very amateurish
admittedly but what the hell, if nature can do it, so I hope can I. So I now have some nut trees. Walnut, Cob nut, Hazelnut and Sweet Chestnut all growing happily and I hope one day to have a double harvest each year. I have also done the same with some stone pine (pinus pinea), Apple (Malus) and Pear (Pyrus) trees.