Does grass grow differently at the edge, inside and outside of a fairy ring?

Details

Grassland fairy rings are circles of vigorous vegetation associated with an expanding underground network of fungal threads. Researchers compared grass and soil at the edge, inside and outside these rings, then used soils from those zones in a controlled greenhouse experiment with Leymus chinensis.

In the field, edge plants had greater aboveground mass and higher nitrogen and phosphorus concentrations than plants inside or outside the rings. Roots inside the rings showed more damage from disease-causing fungi. In the greenhouse, adding live edge soil generally encouraged growth, but lowered phosphorus concentration in aboveground plant tissue—the opposite of the field pattern for that nutrient. Adding soil from inside the ring increased root infection and reduced aboveground plant mass.

These findings suggest that soil organisms contribute to the contrast between vigorous edges and poorer growth inside the rings. The researchers propose that edge microbes make phosphorus more available or stimulate growth directly, and that disease-causing organisms may accumulate as the ring expands. Those mechanisms, including their proposed effects in later growing seasons, remain hypotheses rather than established explanations.