By Molly Murray
UD researcher calls toxic strain of phragmites 'a horticultural
disaster'
The "hit man" of Delaware's marshland -- Phragmites australis -- works
deep within the root zone to silently eradicate any and all competition.

Local scientists now think they have discovered its lethal weapon --
the one laying waste to acre after acre of valuable grasses and other plants
in Delaware and in salt marshes up and down the Atlantic Coast.

It's a toxin secreted below the water line from the plant's roots that
rots away the roots of its rivals, clearing the way for phragmites to
continue their march through native marshland, according to new research by
scientists at the University of Delaware.

The researchers have discovered that a non-native strain of phragmites
that hitched a ride to America hundreds of years ago releases an acid so
toxic it causes the protein structure in nearby plant roots to
disintegrate -- killing off all competition.

"This guy is so bad in terms of what it can do to other stuff," said
Harsh Bais, a plant biologist at UD's Biotechnology Institute. "It's a
horticultural disaster."

The tall, bushy-headed reed is so effective at destroying competing
native plants that it has transformed the mid-Atlantic salt marsh landscape.

Bais said the new research is revealing, but raises more questions:
Does the toxin affect fish and other marsh aquatic life? Are there microbes
that can survive within the acid secretion and play a role in spreading the
toxin? How does the toxin break down in ultraviolet light?

"Every time you answer a question, there is always one remaining,"
said Bais, one of many researchers trying to figure out how phragmites do
their damage -- and maybe how to block them from laying waste to a marsh.

For years, salt marsh ecologists believed there was only one variety
of Phragmites australis and it was so invasive because it spread rapidly by
sending out rhizomes -- creepers that create a thick, impenetrable mat
across the marsh floor.

And because the plant can grow 30 feet tall in a season, it towers
above other marsh plants and forms a sort of canopy that blocks
life-sustaining light from other plants.

But in recent years, researchers along the Atlantic Coast, including
Delaware, have concluded that all phragmites are not equal.

There is a native plant type that would be naturally occurring in
Delaware marshes and a non-native plant that is far more aggressive in
besting the competition.

Researchers have found preserved phragmites rhizomes that date back
3,000 to 4,000 years along Atlantic Coast salt marshes. And there are root
fragments that are 10 times as old that have been discovered in the western
United States.

The root of the problem

American Indians used the native variety reed for everything from
arrow shafts to musical instruments. This native variety isn't an invasive
plant and Bais says it doesn't release the same high level of root toxin as
the non-native variety.

The non-native, researchers believe, was likely introduced to North
America in the late 18th and 19th century when it was brought over with
ballast on sailing ships.

Phragmites produce thousands of seeds but spread mainly with rhizomes,
fragments of which can break off and float downstream along a marsh or be
transported on heavy equipment that has worked in one area and then moves to
another.

Once in a new location, the fragments take root and the invasion is
on.

Thousands of acres of Delaware's marshes are infested with the tall
reeds, which reduce food and habitat for wildlife and change the water flow
and level within the marsh system.

Bais, who is also an assistant professor of plant and soil science in
the University's College of Agriculture and Natural Resources, specializes
in root biology. On this project, he worked with longtime phragmites
researchers John Gallagher and Denise Seliskar at the College of Marine
Studies in Lewes.

Secreted toxin leads the way

Gallagher and Seliskar provided the plant cultures used in the
research, which focused on the root secretions that scientists have long
known existed, Bais said.

The secretions seemed to be important because plants use a great deal
of their photosynthetic energy to create them.

"There's generally a reason" why plants make these secretions, Bais
said.

Researchers -- and home gardeners -- also know that many plants
release harmful chemicals, including walnut and pine trees, ferns and
sunflowers, which produce chemicals that keep other plants from growing in
the same area.

But phragmites are different, Bais said.

They appear to release the toxin not to keep other plants from growing
nearby but instead, to conquer them and spread to new areas in the marsh.

The phragmites toxin is 3,4,5-trihydroxybenzoic acid, a compound also
known as Gallic acid, which is used for leather tanning and in the cork
industry.

"It's nasty stuff," Bais said. "If you get some of it on your skin,
you definitely know it."

When the plant secretes the toxin, nearby plants "have no defense," he
said.

The toxin targets tubulin, a structural protein in the roots of
competing plants. Once the tubulin is compromised, the root breaks down and
the plant dies. "It's almost like falling down," Bais said.

Phragmites, with clear ground ahead and no remaining competition, move
in and take over.

Bais said he and his research team believe the toxin may not be the
only player in the deadly phragmites story.

They are also trying to determine whether a microbe could be working
along with the toxin. In addition, he said, there are questions about how
the toxin reacts under ultraviolet light. Phragmites plants can tolerate
huge amounts of ultraviolet light, and Bais wonders whether this form of
light breaks the toxin down into other potentially nasty chemicals.

"We just don't know the answers yet," Bais said. "But we'd like to
find out."


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