Root responses to soil water gradients in two species of Triodia
The genus Triodia (Poaceae), commonly referred to as spinifex grasses (not to be confused with the coastal genus Spinifex), comprises a distinctive group of perennial, hummock-forming grasses that dominate vast areas of arid and semi-arid Australia. These grasses are particularly emblematic of the inland vegetation across Western Australia (WA), where they play foundational ecological roles. Among the approximately 70 species of Triodia, Triodia schinzii and Triodia pungens are two key representatives within the state’s central and northern drylands, contributing significantly to the structure, function, and resilience of these ecosystems.
Taxonomy and morphological adaptations
Triodia species are well adapted to Australia’s nutrient-poor, drought-prone landscapes. Characteristically, they form dense, hemispherical hummocks, with narrow, sclerophyllous leaves often reinforced with silica bodies. These morphological traits reduce water loss and confer resistance to herbivory and desiccation. Both T. schinzii and T. pungens are C₄ grasses, a physiological adaptation that enhances water-use efficiency under high temperature and irradiance typical of arid zones.
Triodia schinzii, sometimes referred to as "feathertop spinifex", occurs widely throughout the central deserts of WA, extending into the Northern Territory and parts of South Australia. It is typically found on sandy plains and dunes. In contrast, Triodia pungens has a more northerly distribution, thriving on skeletal soils, gravelly rises, and lateritic outcrops of the Pilbara and Kimberley regions. This species is notable for its erect leaf blades that are sharply pointed, hence the species epithet “pungens.”
Ecological importance
The ecological significance of Triodia hummock grasses is multifaceted. Firstly, they form the dominant ground cover in many dryland vegetation types and are key ecosystem engineers. Their hummock structures create microhabitats that buffer against extreme surface temperatures, trap organic matter, and retain moisture — all of which are critical for supporting diverse assemblages of invertebrates, reptiles, and small mammals.
Secondly, Triodia species play an essential role in stabilizing sandy soils and reducing wind erosion. Their extensive root systems bind loose substrates, particularly in dune and swale systems. This function is increasingly relevant in the context of changing fire regimes and climate variability, which may exacerbate land degradation in arid zones.
Fire is an intrinsic ecological driver in spinifex grasslands. Triodia species accumulate large quantities of flammable biomass, and their hummocks burn readily, often leading to extensive but patchy wildfires. However, these grasses are highly fire-adapted, resprouting or regenerating prolifically from seed post-fire. This fire-mediated regeneration not only maintains the dominance of Triodia but also creates temporal and spatial heterogeneity in vegetation structure, which in turn supports a mosaic of faunal communities at different successional stages.
We aim to address the following research questions:
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How do the roots of the two Triodia species respond to vertical soil moisture gradients?
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How do these species respond to sudden rainfall events that rehydrate the topsoil?
To investigate these questions, we are conducting controlled experiments in the glasshouse facilities at the University of Western Australia. We are sampling roots to analyze overall root architecture and preparing root cross-sections for anatomical examination.
This project is a collaboration between myself and Professor Erik Veneklaas at the University of Western Australia. In addition to our joint research efforts, we actively involve thesis students at both the University of Western Australia in Perth and the University of Copenhagen. These student projects provide valuable training opportunities while contributing to data collection, experimental design, and analysis within the broader research framework.
Funded by:
Project: Root responses to soil water gradients
Funding Agency: Carlsberg Foundation
Period: 2 years
Contact
Professor Ole Pedersen
ORCID
Project members:
| Name | Institution | |
|---|---|---|
| Dylan Gibson | The University of Western Australia | |
| Erik Veneklaas (PI) | The University of Western Australia | |
| Kosala Ranathunge | The University of Western Australia | |
| Lukasz Kotula | The University of Western Australia | |
| Ole Pedersen | University of Copenhagen |