Zhao and her team found that samples taken from the center of the ring had higher concentrations of sulfides and less access to nitrogen?"and both conditions limit plant growth. The fairy circles' varying shapes correlated with where nutrients and oxygen were depleted, reports New Scientist. When the researchers added fertilizer to the circles' outer edge, they found little to no difference of growth, but when added to the center of the ring, they found growth where no plants previously were, Science reports.