Pretoria - University of Pretoria (UP) scientists have posited a theory that could explain the tens of thousands of “fairy circles” seen dotted across the arid landscape of Namibia.
These circles have fascinated scientists for decades, and no one knows the actual cause of this phenomenon. (The Nama tribes believed the circles were caused by dragons).
There are many competing theories of their origins – one of which is that micro-organisms could be the missing piece of the puzzle, according to UP researchers. Fairy circles are bare, regularly spaced and sized patches surrounded by grass. Most are between 2 and 5m in diameter, and they occur over thousands of square kilometres in Namibia and into southern Angola.
“These fairy circles are unique to Namibia and southern Angola,” said Professor Don Cowan, director of UP’s Centre for Microbial Ecology and Genomics. Similar “structures” have been found in Australian deserts, but that doesn’t necessarily mean they have the same causative basis.
Cowan said a number of current theories could explain the phenomenon: toxic gases from deep in the soil, toxic chemicals from dead Euphorbia plants, sand termites or the effects of natural plant “self-organisation” processes over long periods.
Each of these major theories is supported by a research group often purporting to have “discovered” the cause. Cowan and his team have investigated the cause of fairy circles and have their own theory. They think that plants growing inside the circles could be dying as a result of phytopathogenesis – the presence of pathogenic micro-organisms (bacteria, fungi or viruses) in the soil. The growth of fairy circles is reminiscent of a growing microbial culture, which is circular and spreads at the margins.
While several other theories can explain plant death, they struggle to explain the growth of the circle itself “To test our theory, we used environmental DNA and modern metagenomic methods to investigate the bacterial and fungal diversity of soils inside the fairy circles, and compared them with control soils outside circles.”
“We found significant differences between these communities, but this is not causative proof. Interestingly, some of the unique fungal species found only in the soils inside the fairy circles are known plant pathogens, though this is also not final proof.”
Cowan said plants germinating inside fairy circles, after rain, die quickly and seem to be more susceptible to drought. This implies the causative agent is somehow related to root function.
“Fairy circle structures might be caused by sand termites eating roots in one desert area, while residual toxins in the soil from dead Euphorbia plants might be the cause in another, and pathogenic fungi in a third.”
The circles appear to have a lifespan – they seem to expand with the death of grass plants around the outer margin (which makes the circle larger)
Plants around the edges of the circles grow taller and stronger than those on the outside, until they die as the circle expands.
“Interestingly, no one seems to report ‘newborn’ or very small fairy circles.”
Pretoria News