The contribution of pathogenic soil microbes to ring formation in an iconic Australian arid grass, Triodia basedowii (Poaceae)

Abstract

Ring-forming species of spinifex grasses (Triodia spp.) are a dominant feature across much of Australia's arid and semi-arid zone. Researchers have long been curious about the mechanisms underpinning their striking growth form. However, none of the factors investigated to date provide a convincing explanation for ring formation. Here, we asked whether an accumulation of pathogenic soil microbes might impede seedling emergence and subsequent growth in the centre of Triodia basedowii rings. We collected soil from inside and outside naturally occurring spinifex rings and compared plants grown in soil with live microbes to plants grown in sterilised soil. Consistent with our hypothesis, we found that emergence of T. basedowii seedlings was lower in live soil from inside the rings than in live soil from outside the rings. Further, seedling emergence in soil from inside the rings increased significantly in response to soil sterilisation. We found no significant difference in growth between sterile and live soils. However, this might be due to a lack of power caused by high rates of seedling mortality in all treatments. Overall, our study provides evidence for the role of soil pathogens in shaping this iconic Australian grass.