Australia: The Land Where Time Began

A biography of the Australian continent 

The impoverished nature of Australian soils makes life difficult for plant life over most of the continent. One way to overcome the problems of nutrient deficiency is to form symbiotic associations with other organisms such as fungi and bacteria. Mycorrhiza are associations with fungi. The types of mycorrhizal association are arbuscular, ectomycorrhiza, ericoid and orchid. As well as being important in the survival of many plants, especially on impoverished soils, and they help bind soils, it has now been found that they even regulate biodiversity. Mycorrhizas pass soil nutrients on to their host in exchange for carbohydrates that are more difficult to find in the soil, and they would need to compete with soil bacteria for carbohydrates in the soil. Orchid mycorrhizas are an exception, where the nutrients and carbohydrates are passed on to the orchid, with no known return to the fungus. It's almost like the plant is a parasite of the fungus that infected it.

Groups of plants tend to associate with particular types of mycorrhizas, though some, such as eucalypts, form associations with both arbuscular mycorrhizas and ectomycorrhizas. The fungi have a very wide range of plant species they can associate with. The various types of mycorrhizas form in the host roots. The ways they contribute to plant growth, and each type is at least partially specific to a particular set of environmental conditions.

Sources & Further reading

Mary E. White, Earth Alive, From Microbes to a Living Planet, Rosenberg Publishing Pty. Ltd., 2003

• Arbuscular Mycorrhizas
• Ectomycorrhizas
• Ericoid Mycorrhizas
• Orchid Mycorrhizas