Why do forest plants (spruce, pine, birch) take root better if they are planted together with the mycelium

Why do forest plants (spruce, pine, birch) take root better if they are planted together with the mycelium of cap mushrooms?

Forest plants (trees) take root better if they are planted with a mycelium of cap mushrooms, because plants and mushrooms, in this case, enter into symbiosis – mutually beneficial cooperation. The mycelium tightly braids the roots of plants, pulling mineral salts and water to them. And the tree gives the mycelium the organic substances it needs. An additional positive property for the tree is that the mycelium secretes special substances similar to antibiotics, and this increases the tree’s resistance to disease.