Final answer:
The correct term for the association between a fungus and a tree root is mycorrhiza, a symbiotic relationship that enhances nutrient and water absorption for the plant and provides carbohydrates for the fungus.
Step-by-step explanation:
The term that describes the close association of a fungus with the root of a tree is mycorrhiza. This symbiotic relationship, where the fungus colonizes the plant roots, is beneficial to both organisms. The plant provides carbohydrates produced through photosynthesis to the fungus, while the fungus extends the root's water and mineral absorption capabilities through its large surface area of mycelia and hyphae.
In the mycorrhizal partnership, there are several types, including ectomycorrhiza, which involves a fungal mantle around the roots, and arbuscular mycorrhiza, where the fungi penetrate the root cells to form a network. This mutualistic association is essential for the plant's nutrient uptake, particularly in nutrient-poor soils, and is key to the survival and health of many terrestrial plants.