Trickle down just as nature has done for eons - most vegetables only have roots extending .5 meter or less.. And plant roots themselves, as they die, are carrying large amounts of nutrients downward. Mushroom mycelium(layman: "roots") often extend a few feet into the soil and help prevent the further trickle down of micronutrients. Most people don't get that with the exception of a few types that attack trees, mushrooms are awesomely good for plants and primarily consume stuff plants can't consume without their help. They are "primary composters" of organic material, plants are secondary. *You find mushrooms in your garden, throw them in a blender with some water, then water the garden to spread them. Your plants will thank you.