Much of Australia has extremely impoverished soil. Phosphate is particularly deficient. The major difficulty in revegetating these soils after severe disturbance is that plant survival and growth is unpredictable. Mycorrhizas are associations between soilborne fungi and the roots of plants. Of particular interest are the arbuscular mycorrhiza (AM) whose fungi form an internal colony in the roots of some 70% of all plant species. In AM, the fungi function as extensions of the root system, enabling the plant to increase uptake of non-labile minerals, especially phosphorus (P), from soil. The fungus gains its organic energy from the plant, and can only be maintained in the presence of living roots.