In the soil, roots encounter shreds of fungi with which they form mycorrhiza - a mutually beneficial symbiotic relationship.

An excerpt from the article 22 facts about Trees

Some fungi are specific to only one tree species, while others associate with multiple species. The tree obtains minerals from the mycelium, and the mycelium obtains carbohydrates, which are products of photosynthesis. Mycelial tufts can connect different trees to form a network, carrying nutrients and various types of information.

Fungi promote root growth and help protect trees from predators and pathogens. They also protect trees from pollution by accumulating heavy metals in their tissues. Fossil evidence indicates that the relationship between tree roots and mycorrhizal fungi has existed since the early Paleozoic, four hundred million years ago, when the first vascular plants colonized dry land.