Life Science Fairy circles: New study says microbes, not magic, are their makers

Fairy circles: New study says microbes, not magic, are their makers

Fairy circles in Namibia have been blamed on dragons, termites, plant warfare and now microbes. Photo: Professor Norbert Juergens
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For more than 100 years, scientists have been trying to solve the mystery of fairy circles – flattened circles of earth ringed with grasses, like eyelashes.

When seen from above, they render a landscape with a spectacular honeycomb pattern.

They were originally discovered in the Namibian desert, where the locals long believed they were the work of dragons.

Since then, rival theories having been popping up at an increasing rate as time goes by.

Grazing ants, radioactivity, subterranean poisonous gases, termites and plants fighting among themselves for water resources have all been investigated and argued over.

Fairy circles were first discovered in Western Australia in 2014. Photo: Stephan Getzin

In 2014, researchers lost their minds when fairy circles, fringed with spinifex, were found in Western Australia and Northern Territory – although local Indigenous people say they were long used as places to sit and grind grasses, because of their flat, hard surface.

Now, Sydney researchers believe microbes are to blame.

Bugs in the soil are strangling seedlings

Researchers from the University of NSW have found “an accumulation of pathogenic soil microbes might impede seedling emergence and subsequent growth in the centre of spinifex rings”.

The scientists tested the idea by collecting soil from inside and outside spinifex rings and planting each sample with spinifex seeds.

As expected, the soil from outside the rings grew more seedlings than the soil from inside.

Then did something interesting: They sterilised the soil from inside the rings, killing all microbes.

“Consistent with our hypothesis, we found that sterilising soil from the inside of spinifex rings significantly increased spinifex seedling emergence,” said Professor Angela Moles, co-author of the new paper and director of UNSW Science’s Evolution & Ecology Research Centre.

Their results suggest that “die-back” in the centre of spinifex plants might be explained “by older parts of the plant succumbing to a build-up of pathogenic soil microbes through time”.

However, new seedlings tend to establish more at the outside edge of the rings where there are fewer pathogens in the soil.

“Most people tend to think of the beneficial effects of microbes on plant growth,” Professor Moles said.

“However, sterilising soil actually makes most plants grow better. That is, the negative effects of the pathogenic microbes tend to outweigh the positive effects of the beneficial microbes.”

Professor Moles said this new information helps scientists further understand the unique ecology of Australia’s dry grasslands, and adds to the growing recognition of the crucial function that soil microbes play in terrestrial ecosystem processes worldwide.

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