The Value of Best Friends for a Plant in the Tropics

Your average plant would not survive without fungi.  In all regions of the world and among almost all plants, mycorhizzal fungi essentially are socks.  As you would cover your feet with a sock, plants cover their roots with fungi.  However, while socks can wick moisture and keep you warm, mycorhizzal (my-co-rise-uhl) fungi provide plants with vital and otherwise unobtainable nutrients.

Matthew E. Smith, assistant professor and curator of fungal herbarium at University of Florida, knows a lot about fungi and tropical rainforests.  Knowing about fungal associations for tropical plants can be useful, and he addressed the ecological importance in a seminar.

Not likely a South American orchid, but a pleasant example nonetheless (Photo credit: donsutherland1).

Ever heard about the early days of orchid cultivation?  Wealthy Europeans wanted exotic orchids from South America, but even the best horticulturalists couldn’t keep the plants alive.  Whenever Europeans wanted more orchids, botanists had to travel to South America and collect them from the wild.

That is until a German scientist compared soils from the two locations and found string structures of fungi among the orchid roots from South America.  As long as the fungus was transplanted with the orchid, the flower flourished.

Sun, water, soil and mycorhizzal fungi are all you need to grow a plant.

Fortunately, these fungi entwine among root cells, even penetrating them.  As long as the native soil is not thoroughly washed from the plant, the fungi will usually stay intact.

Biologists have documented few fungi species in the tropics.  Most fungi and their relatives, or lineages, are unknown. Smith identifies these organisms for researchers and crop farmers in different world regions. He said he sought to study what and where few had before him.

“We looked at world regions and distributions of lineages to see where more information was needed,” Smith said.

National Science Foundation funded Smith’s expedition to Guiana Shield, a region in northern South America.  Although not technically the same region sometimes glorified as “the lost world,” it is very close.

Smith said finding fungi was difficult. The organisms’ visible portion, the fruit or what most people think of as a mushroom, was not always available. Fruiting occurs seasonally or at one time interval every couple of years.

Smith said his team relied on molecular samples of fungi collected from root tips in order to identify species and relationships. The team tested samples against a database of other researchers’ collections.

“In-depth molecular sampling is important,” Smith said. “In the forest you see fungi, but molecular sampling allows us to see without fruiting bodies.”

An example of a fruiting body that is not found in a grocery store.
An example of a fruiting body that is not found in a grocery store.

Smith said Guiana Shield has diverse lineages that evolved in isolation. Fungi have few relatives outside their respective lineages and many more lineages of isolated regions may need documentation.

Much like the orchid, plants native to these areas are not likely to grow well in gardens or farms without the fungi found in their native soil.  They are familiar with certain species of fungi and will not readily establish new relationships with unfamiliar fungi species.

Some mycorrhizal fungi survive dependent on a single species of plant and vice versa. Other fungi and can support and be supported by different plant species.  Either way, the plant-fungi combo must establish a linkage between roots and hyphae, or fungal roots, to feed each other the half of their diet they cannot provide for themselves.

In the orchid’s case, the plant had a hard time establishing in foreign soil without its other half.


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