That’s where mycorrhizae fungi are handy. Both the host plan/tree and the fungi create a symbiotic relationship by fusing the roots with the mycelium hyphae. The fungus extracts minerals that the tree can’t “digest” and in return the tree “feeds” the fungus with its own sugars present in the sap.
Don’t forget that plants get their energy through photothinsesis, mushrooms can’t do this, so they have to break up matter looking for sugars.
There can also be an indirect beneficial situation when you have a saprophytic species like the Oyster Mushroom Pleurothus ostreatus that break down matter into something that the plants can use to their benefit. That’s why fungi are so important. Without them there would be no soil just rubbish and piles of dead matter once bacteria had their share.
I have yet to find a fungus or fungi that could be paired up make the perfect crop 
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Image the following:
@Sebring after all his hard work of experiments and seed runs ends up with shitload of vegetable matter. Instead of mulching he can dry it like straw. Once dried he can go to the nearest coffee shop and local restaurants and gather spent coffee and on the way he collects some old cardboard boxes. He gets home and pasteurizers the straw. Once it cools down he mixes all the ingredients and last but not least the spawn. Wrap it all up and protect from dry air and sun so the mycelium can take over. He can do this in a laundry basket or other vessel as long as ther can be some breathing. Alternatively this mix can be buried in the ground where you wish.
In the case of the basket if moisture is ideal, it should take about a couple of weeks for the mushroom to take over the media. If you mist the basket pinning should start and you mushrooms start forming. Once the media is spent which usually happens after 3 flushes (think crops) of mushrooms you end up with a yummy substrate for your plants.
Have a look at Paul Stamets books about mushroom cultivation. He has many books about mushrooms: gourmet and medicinal, magic mushrooms, permaculture and mycoremediation.
There is also a guy called RogerRabit that has a series of videos in which he shows how to prepare the above Tek and other ones. I think it’s called “Let’s do mushrooms” sorry I’m a little rusty when it comes to names 