Monday, August 27, 2007

Corallorhiza maculata

In the Rocky Mountains, spotted coralroot, Corallorhiza maculata, is most
commonly found in stands of ponderosa pine and lodgepole pine. In eastern
deciduous forests, it is associated with beech trees, and in California and
Oregon it grows beneath oaks.

It is a perennial plant with stems one to two feet tall, bearing eight to
20 flowers. Leaves... narrow, transparent sheaths that cling to the stems.
Stems are purple to reddish-brown, and the small... flowers have white
petals with fuchsia spots. Some populations have albino plants, with yellow
stems and unspotted flowers.

Spotted coralroot... lack of leaves, it has no roots, and it lacks
functional chloroplasts, so it cannot photosynthesize. Instead of roots, it
has a fleshy, branched rhizome that looks like a soft coral ? hence the
common name coralroot.
Ponderosa pine and lodgepole pine have mutually beneficial associations
with ectomycorrhizal fungi that grow on their roots. Spotted coralroot
grows beneath ponderosa pine and steals sugars from the tree that shades it.

Ectomycorrhizal fungi serve as extensions to the root system, greatly
enhancing the tree's access to water, nitrogen and nutrients that do not
diffuse well, such as various forms of phosphate.... the fungus takes
sugars from the roots of the pine. Sugars are produced in the crown of the
tree by photosynthesis, and are transported to the root system for storage.

Ectomycorrhizal fungi and pines depend on one another. The fungi obtain all
of the photosynthetic products food from pine roots, and if they are
separated from the roots they wither. Pines grow poorly if they are
deprived of ectomycorrhizal fungi and are much more susceptible to drought.

Spotted coralroot taps into the mutualism between fungus and pine. The
orchid's fleshy rhizome attaches to the fungus, and it extracts water,
nutrients and sugars. Water and nutrients are taken directly from the
fungus, but the orchid uses the fungus as a bridge to take sugars from the
pine. This is a parasitic relationship, for neither the fungus nor the tree
derives any benefit from the orchid.

Ponderosa pine is host to many species of ectomycorrhizal fungi, but
spotted coralroot parasitizes a small number of fungal species, and the
species parasitized vary among environments. For example, coralroot uses
one set of fungi in oak forests, and a different set of fungi in ponderosa
forests. Similarly, coralroot uses one set of fungal species at high
elevations and a completely different set at low elevations.

... Reddish-brown and albino coralroots grow intermixed in a population,
but these two forms parasitize different fungal species."


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