Microbial Factors May Contribute to the Persistence of Australian Fairy Circles

Abstract

Fairy Circles (FCs) are roughly circular, spatially periodic barren patches occurring both along the southwestern African coast, spanning the Namib Desert (NFCs), and in the Pilbara region of Western Australia (AFCs). The origin of both NFC and AFC patterns is still debatable and a subject of ongoing research. Recently, it was argued that pathogenic soil microbes may contribute to ring formation of the Triodia basedowii grass which is the same grass species that forms the AFCs. We have analyzed, under controlled laboratory conditions, soil samples taken from different parts of AFCs (center, periphery and m3atrix) for microbiological activities by Lettuce germination experiments under different manipulations. In seven different circles, out of an average of 13, root lengths of germinated seeds were strongly inhibited in the samples taken from the center, and to a lesser extent, in the samples taken from the periphery and the matrix. Quantitative analyses of the soil microbial community from the FC center found no support to the hypothesis that phytotoxic effect was caused by soil crust cyanobacteria due their low abundance. However, in soil of the FCs it identified both heterotrophic bacteria and fungi that may contribute to the phytotoxic effect. Although our study was not done with seeds of Triodia basedowii it supports the idea that microbial activities in the soil may contribute to AFC persistence by inhibiting plant germination and development in the bare soil gaps in addition to the physical soil crusts resulting from weathering. This suggests that negative plant-soil feedback can act in concert with the main driver mechanism of the AFCs, the scale-dependent plant-water feedback.