By Staff Reporter
Pretoria, April 3 — Scientists from the University of Pretoria (UP) have proposed a theory that could explain the cause of the “fairy circles” found throughout the arid landscapes of Namibia. These circles have intrigued scientists for years, and no one knows their actual cause, with many theories competing to explain them. One such theory, proposed by UP researchers, suggests that microorganisms may be the missing piece of the puzzle.
Fairy circles are patches of bare, regularly spaced ground, surrounded by grass, which range from 2 to 5m in diameter, and are scattered over thousands of square kilometres in Namibia and southern Angola. Professor Don Cowan, director of UP’s Centre for Microbial Ecology and Genomics, said that while similar “structures” have been found in Australian deserts, that does not necessarily mean they have the same causative basis.
Cowan said that several current theories could explain the phenomenon, including 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. Cowan and his team believe that plants growing inside the circles could be dying as a result of phytopathogens – the presence of pathogenic micro-organisms (bacteria, fungi, or viruses) in the soil.
The team’s theory is that the growth of fairy circles is similar to a growing microbial culture, which is circular and spreads at the margins. Cowan said that, while several other theories can explain plant death, they struggle to explain the growth of the circle itself. To test their theory, the researchers used environmental DNA and modern metagenomic methods to investigate the bacterial and fungal diversity of soils inside and outside the fairy circles. They found significant differences between these communities, including unique fungal species found only in the soils inside the fairy circles, which are known plant pathogens.
Plants germinating inside the circles, after rain, die quickly and seem to be more susceptible to drought, which implies that the causative agent is somehow related to root function. Cowan said that fairy circle structures might be caused by sand termites eating roots in one desert area, residual toxins in the soil from dead Euphorbia plants in another, and pathogenic fungi in a third. The circles seem to have a lifespan and expand with the death of grass plants around the outer margin, making the circle larger.
Interestingly, no one seems to report “newborns” or very small fairy circles. Fairy circles are unique to Namibia and southern Angola and have fascinated scientists for decades, but Cowan and his team believe that their theory of the role of pathogenic micro-organisms in their creation could be the answer to this mysterious natural phenomenon.
– Namibia Daily News