Cyanide levels near fairy rings affect the growth of grasses and fungi

Abstract

Field and laboratory experiments were conducted to test the hypothesis that cyanide produced by Marasmius oreades (Bolt ex Fr.) Fr., and further concentrated by a decrease in soil moisture near fairy rings, would reach levels inhibitory to grasses and soilborne fungi. Soil water content, cyanide levels per gram dry mass of soil, and micromolar concentrations of cyanide in soil solutions were determined for two fairy rings at five dates. Within 50-60 cm of the rings, increases in soil water and decreases in cyanide per gram dry mass of soil led to a steep decline in cyanide concentrations with distance from the rings. Seven fungi and four turfgrasses were exposed to different cyanide levels in vitro to estimate the cyanide concentration required to reduce fungal biomass or grass root length by 50% (EC50). These EC50 values were then compared with the observed cyanide concentrations in soil solutions near fairy rings. Within 25 cm of the rings, cyanide concentrations were sufficiently high to inhibit grass root growth and greatly inhibit the growth of some fungi, while having a negligible effect on others.Key words: cyanide, Marasmius oreades, fairy ring, turfgrass.