In The Orchid Thief, writer Susan Orlean describes the cultlike devotion that these exotic-looking flowers inspire among plant collectors. One reason, in addition to their beauty, that orchids are so prized is that they are fragile: although they grow in every U.S. state and on every con­tinent except Antarctica, many are endangered, and the flowers are exceed­ingly sensitive to environ­mental changes. Native orchids’ dustlike seeds will grow only if nourished by certain groups of root fungi, known as mycorrhizal fungi.

Little is known about these organisms—so little that many have not been named. They grow into the roots of orchids, which digest the fungi to obtain needed nutrients. Recently a four-year study has shed new light on where my­corrhizal fungi grow and under what conditions they stimulate orchids to germinate. The results, published online Jan­uary 24 in Molecular Ecology, will help ecol­ogists preserve rare or­chid varieties.

The team of researchers, led by ecologist Melissa McCormick of the Smithsonian Environ­mental Research Center in Edgewater, Md., planted and tracked three U.S. orchid species—all present in the East and endangered somewhere in the country—in six study sites: three in younger forests, which were 50 to 70 years old, and three in older forests, which were 120 to 150 years old. Investigators covered each plot with leaf litter, decomposing wood or nothing and provided half the plots with the specific fungi known to promote growth in each orchid.

The researchers also identified the existing fungi in each forest. Because the organisms have no fruiting structures, they can be tough to detect, so the team pio­neered the use of testing for DNA in the soil to identify where and how much fungus was present. Older forests, McCormick and her colleagues found, had about five to 12 times more orchid-friendly fungi than younger forests, and the fungi in older forests were more diverse.

Each orchid had different requirements to grow. For Goodyera pubescens (a stalk of its small white flowers is pictured), only older forests held enough fungus for it to flourish. Adding the fun­gus to younger forests alone or in combination with decom­posing wood did not make Goodyera seeds germinate. The host fungus of Tipularia dis­color, which has many small mauve-purple flowers with yellowish centers, was wide­spread in young and old forests alike but could support germi­nation only on decom­posing wood. The host fungus for Liparis lilii­folia wasn’t common in the wild, but the orchid would germinate if the fungus was added.

Orchid conservation plans gen­erally do not account for orchid fungi abundance or require-ments, simply because the techniques and knowledge to identify the fungi haven’t been in place. Says McCormick, “We’re hoping others can apply these tech­niques to figure out what environmental conditions affect the fungi.”

This article was published in print as "Picky Eaters Club."

8 Comments

1. 1. DAD1945 02:36 PM 3/24/12

   I don't typically comment, but this article had some inaccuracies.
   
   Orchid roots do not digest mycorrhizal fungi. The fungi are digesting the organics in the soil and converting them into a soluble nutrient form for plants to uptake. Two types of mycorrhizae are recognized, either ectotrophic, covering the surface of the root, or endotrophic, living inside the root. The relationship is quite complex appearing to be a mutually beneficial symbiosis.
   
   Mature forests have more fungi than younger ones. Not surprizing if you understand the ecological conditions required by each type of plant community, the succession of one community into another, the micro-(and macro) environmental changes produced by each successive plant community, the new, old and ever changing environmental niches in each community, and the individual requirements of any one of the plants either in the community, or attempting to move in. (such as light, water, available nutrients, etc.)
   
   I appreciate the work that the microbiologists are attempting to perform. An introductory course in Ecology would broaden their insight.

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2. 2. vincenzi 11:05 AM 3/25/12

   As a scientist by training and grower of orchids by passion, I have always questioned the so-called symbiotic relationship between orchids and mycorrhizal fungi. Yes, it is clear that orchids benefit from the relationship, but what is the benefit to the fungi get in return? Every time the mycorrhizal topic arose at a meeting of our local orchid society, usually a presentation by some expert orchid grower, I would ask the question. So far, no satisfactory answer. Perhaps Dr. Madren or one of the readers can help.
   

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3. 3. McCormick 10:58 AM 4/10/12

   Actually, while most plants have a two-way exchange of nutrients across a membrane, orchids actually DO digest digest their mycorrhizal fungi. There are a lot more than two types of recognized mycorrhizae, with orchid mycorrhizae being one type. The authors of the article are ecologists (not microbiologists) who have spent over a decade studying orchid-fungal associations.

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4. 4. McCormick 11:00 AM 4/10/12

   In response to vincenzi, there is currently no good explanation of what the fungi get out of the association with orchids. There is one study that suggests the mycorrhizal fungi can get some benefits from the orchids they associate with, but many other studies have tried to demonstrate such a benefit and failed.

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5. 5. seanacoy 12:13 AM 4/14/12

   The implication is that the geography of orchids is restricted to some degree by the availability of particular fungi groups. How many such groups are there? What happens when ecological changes alter the fungi groups? Do local orchid species die out or adapt? Do alien orchid species move in? If orchids are so prevalent and varied (20,000 or more species) and widespread, did the fungi play any rôle spread or speciation of orchids?

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6. 6. Quinn the Eskimo 10:12 PM 4/22/12

   I don't know about orchids. But, I've got some great dandelions you can have -- cheap.

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7. 7. RafaelF.Markham 04:44 AM 5/15/12

   Thumbs up guys your doing a really good job.
   <a href="http://www.agaricusbm.org/no/hjem.html/"> agaricus blazei murill </a>

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8. 8. RafaelF.Markham 04:45 AM 5/15/12

   <a href="//www.agaricusbm.org/no/hjem.html/"> agaricus blazei murill </a>

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