a type of fungus (= an organism that gets its food from decaying material or other living things) that lives on the roots of a green plant, where each of them helps the other to grow well

Mycorrhizae are fungi that form a relationship with plant roots and increase their ability to take up nutrients from the soil. 菌根是一种真菌，能与植物根系形成一种关系，提高植物从土壤中吸收养分的能力。

the symbiotic relationship (= involving two types of animal or plant in which each provides the conditions necessary for the other to continue to exist) between a fungus (= an organism that gets its food from decaying material or other living things) and the roots of a green plant

Many plants have fungi in or on their roots forming associations called mycorrhizas, which serve a similar function to root hairs. 许多植物的根内或根上都有真菌，形成称为菌根的共生关系体，其功能与根毛类似。