Australia: The Land Where Time Began

A biography of the Australian continent 

Orchid Mycorrhizas

The orchids possess tiny non-photosynthetic 'dust seeds', that can be for a short seedling stage, though is some cases it can persist throughout the life of the plant, from germination to flowering. The result is that the host plant is unable to provide carbohydrates to the associated fungi, requiring the fungi to provide both sugar and nutrients. As occurs with other mycorrhiza, the fungal hyphae penetrate the cell walls of the roots and form tightly coiled hyphae in the cells that are surrounded by the cell membrane, increasing the surface area for sugar and nutrient exchange, the difference being, in this case it is one-way, from fungus to plant. Some of the orchid mycorrhiza are saprophytic fungi, obtaining carbohydrates by the breakdown of the leaf litter in the soil. Some form associations with plants such as trees to obtain their carbohydrate. In this case, as well as in the saprophytic types, some carbohydrate is passed on to the orchid.  In effect, the orchid is a parasite of both the fungus and the tree.

An orchid that is linked to a photosynthesising plants by a fungal mycorrhiza is the Western Australian ground orchid, that gets all its sugars from Melaleuca trees via the fungal mycorrhiza. This orchid spends it entire life below the soil surface, even its flowers are subterranean, being pollinated by slugs. It is unknown if the fungi in such associations gain any benefit, or why they persist in playing intermediaries between the orchid and a photosynthising plant.

Sources & Further reading

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

 
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading