Australia: The Land Where Time Began
in the Kwongan Sandplain Flora
In the South-west Province of Western Australia, of the 9 genera of sedges (Cyperaceae), 7 produce dauciform roots, clusters of carrot-shaped rootlets that are densely covered with root hairs. They also occur in the regions of South Africa with a Mediterranean-type climate.
These are produced by Restionaceae, operating in a similar manner to the finely branching cluster rootlets of other species from the South-West Province. Capillarity is increased in these rootlet clusters, the result being that the soil remains damp which allows the uptake of water and nutrients for longer than would otherwise be the case. Restionaceae have a dual root system, tap roots with sparse branches, that penetrate deep into the soil, and near the soil surface, many thin cluster root that are highly branched.
Among the plants of the Kwongan flora, symbiotic mycorrhizal associations are ubiquitous in plants that lack proteoid roots. Fungal symbionts of genera of the Endogonaceae, primitive fungi that are obligate symbionts, Glomus being the commonest. Each species of fungus is believed to have a wide host range. Infection of the plants roots by the mycorrhizal fungi is usually by penetration of the hyphae, which are widespread in the soil, though the fungal spores survive in the soil, accounting for some root infections. Because of the network of hyphae in the soil it is also possible for some plants in a community to become epiparasitic, directing nutrients away from plants connected to the network that are less efficient. There are no aggressively dominant species in the Kwongan communities, the nutrient sharing via the fungal networks being an alternative strategy, dominance by stealth. The level of mycorrhizal symbiosis increases as the soil fertility decreases, and in parts with the highest level of interspecific competition. Where symbionts are concentrated, the largest amounts of zinc, potassium and sulphur are available to the plants.
|Kwongan Sandplain Flora, Western Australia
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading