Mycorrhizae Fungi also form mutualistic relationships with plant roots. Almost half of the tissues of trees are hidden beneath the ground in masses of tangled roots. These roots are woven into a partnership with an even larger web of fungal mycelia. These symbiotic associations of plant roots and fungi are called mycorrhizae (my koh RY zee; singular: mycorrhiza).

Scientists have known about this partnership for years, but recent research shows that it is more common and more important than was previously thought. Researchers now estimate that 80 to 90 percent of all plant species form mycorrhizae with fungi. The hyphae of the fungi form a network associated with the roots of the plants and extending into the soil. The hyphae collect water and minerals and bring them to the roots, greatly increasing the effective surface area of the root system. In addition, the fungi release enzymes that free nutrients in the soil. The plants, in turn, provide the fungi with the products of photosynthesis.

The presence of mycorrhizae is essential for the growth of many plants. The seeds of orchids, for example, cannot germinate in the absence of mycorrhizal fungi. Many trees are unable to survive without fungal symbionts. Interestingly, the partnership between plant and fungus does not end with a single plant. The roots of each plant are plugged into mycorrhizal networks that connect many plants. What's more astounding is that these networks appear to connect plants of different species.

In Your Notebook Make a graphic organizer that illustrates the flow of materials between a fungus and a plant in a mycorrhizal symbiosis.

Table of Contents