What causes the phenomenon known as fairy ring?

Fairy rings are a fascinating natural phenomenon primarily caused by fungi. As these fungi grow, they expand in a circular shape, leading to the characteristic ring formation. The process involves the mycelium, which is the vegetative part of the fungus, spreading out in a radial pattern. Over time, as the fungus depletes nutrients in the soil at its center, the grass or vegetation in that area may die off or appear less healthy, while the outer edges of the ring remain lush and green due to the access to more nutrients.

The relationship between fungi and soil nutrients is crucial here; the fungi break down organic matter, releasing nutrients that promote grass growth in those outer regions. This results in visible rings or circles of green, distinguishing it from surrounding areas. Other choices, although related to different aspects of plant health or soil conditions, do not directly lead to the specific formation of fairy rings as fungi do. Understanding this aspect of fungal growth helps clarify the ecological role fungi play in various environments.