fairies keep their plants on a tight leash

Beneath the piercingly blue skies of the northern Mongolian steppe, the evidence of fairy activity is plain for all to see. While historically the subject of myths and folklore in medieval European cultures, scientists have recently taken an interest in the mysterious “fairy rings” that occur in woodlands and grasslands across the globe.

What, exactly, is a fairy ring? The term “fairy ring” refers to a ring, ribbon or arc of mushrooms that are the fruiting bodies of an single fungal organism, which branches, just beneath the soil surface, into a mire of thread-like mycelium. That much about fairy rings is relatively straightforward. As research on fairy ring ecology progresses, however, it is becoming clear that the interactions between these fungi and the plants the interact with are incredibly complex and varied.

A typical fairy ring as seen from above ground

Fairy ring fungi can be broadly divided into two classes. “Tethered” fairy rings consist of fungi which form symbiotic associations with tree roots, accessing nutrients for their host tree and gaining carbon in return. Free fairy rings, which occur largely in meadows, do not necessarily work cooperatively with neighboring plants. These fungi produce secrete a broad range of chemical compounds that either stimulate or inhibit the growth of grasses.

Lepsida sordida is one of the most well-studied fairy ring forming fungus, occuring naturally throughout many northern temperate zones. Researchers have identified the chemical compound “AHX” released by L. sordida that acts to stimulate plant growth so strongly that its use in agriculture has been seriously considered. When rice or potatoes are cultivated with a small amount of AHX, the grain yield per plant increased by 25-40%!

Now a group of researchers has revealed another surprise capability of L. sordida– a compound termed “ICA” that also exerts influence over plant growth. In controlled experimental additions, ICA inhibits the growth of grass shoots and roots. This growth-inhibitory effect was also observed when ICA is added to lettuce and rice seedlings.

A plant-growth regulating compound was isolated from a fairy ring forming fungus, Lepista sordida, and its chemical structure was identified as imidazole-4-carboxamide (ICA). Credit: Choi et al. 2010, "Plant-Growth Regulator, Imidazole-4-Carboxamide, Produced by the Fairy Ring Forming Fungus Lepista sordida"

It seems that through the evolution of very specific plant regulatory molecules, fairy rings are able to shape their local environment to suit their needs. The age-old superstitions describing mysterious and sometimes deadly powers of fairy rings  may yet contain some truth.

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