 L. indigo is a mycorrhizal fungus , and as such , establishes a mutualistic relationship with the roots of certain trees ( " hosts " ) , in which the fungi exchange minerals and amino acids extracted from the soil for fixed carbon from the host . The subterranean hyphae of the fungus grow a sheath of tissue around the rootlets of a broad range of tree species , forming so @-@ called ectomycorrhizae — an intimate association that is especially beneficial to the host , as the fungus produces enzymes that <unk> organic compounds and facilitate the transfer of nutrients to the tree . 
