Changing climate likely to make 'super weed' even more powerful

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Harsh Bais (left), University of Delaware assistant professor of plant and soil sciences, and Thimmaraju Rudrappa, a former UD postdoctoral researcher who is now a research scientist at DuPont, examine specimens of Phragmites. The UD team has found that this top invasive plant delivers a one-two chemical knock-out punch to snuff out its victims, and the poison becomes even more toxic in the presence of the sun's ultraviolet rays. Credit: Kathy F. Atkinson/University of Delaware

Researchers at the University of Delaware have discovered a new reason why the tall, tasseled reed Phragmites australis is one of the most invasive plants in the United States.

The UD research team found that Phragmites delivers a one-two chemical knock-out punch to snuff out its victims, and the poison becomes even more toxic in the presence of the sun's ultraviolet rays.

The study, which is published in the June issue of the scientific journal Plant Signaling & Behavior, is believed to be the first to report the effects of UV-B radiation on plant allelopathy, the production of toxins by a plant to ward off encroachment by neighboring plants.

The authors include Thimmaraju Rudrappa, a former postdoctoral researcher at UD who is now a research scientist at the DuPont Company; Harsh Bais, assistant professor of plant and soil sciences; Yong Seok Choi, postdoctoral researcher in the Department of Chemical Engineering; Delphis Levia and David R. Legates, both associate professors in the Department of Geography; and Kelvin Lee, Gore Professor of Engineering and director of the Delaware Biotechnology Institute.

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These micrographs show, at left, untreated Arabidopsis roots, and on the right, roots treated with mesoxalic acid, one of invasive Phragmites' weapons. Note the degradation of actin, a plant structural protein, in the right photo. Credit: Thimmaraju Rudrappa and Harsh Bais/University of Delaware

"The toxin secreted by Phragmites is degraded by sunlight -- ultraviolet rays -- and causes severe deleterious effects on other native plants," Bais said.

"Our research also addresses the growing questions of increased UV-B incidences because of global warming and its ultimate effect on plants. In this case, an invasive plant is accidentally utilizing the changed global conditions for its survival and invasion," Bais noted.

Two years ago, Bais led a study which discovered that Phragmites actively secretes gallic acid to kill off plants and take over new turf. Gallic acid, also known as 3,4,5-trihydroxybenzoic acid, is used for tanning leather, making dyes and inks, and formulating astringents, among other applications.

In this research, the scientists found that the gallic acid released by Phragmites is degraded by ultraviolet light to produce another toxin, mesoxalic acid, effectively hitting susceptible plants and seedlings with a double-whammy.

The mesoxalic acid triggers a similar "cellular death cascade" in victim plants as gallic acid does, Bais said, destroying the tubulin and actin, the structural protein in the roots, within minutes of exposure.

The scientific team detected the biological concentrations of mesoxalic acid in Delaware wetlands, in stands of both exotic and native Phragmites australis. The study highlights the persistence of the photo-degraded phytotoxin, particularly potent in the exotic species of the plant, and its enhanced effects against the native species of Phragmites, which is becoming increasingly endangered in the United States.

Walnut trees, pine trees, ferns and sunflowers are among the plants that release harmful chemicals to prevent other plants from growing too close to them.

However, Phragmites uses this strategy not so much to keep other plants away, but to aggressively conquer them and invade new territory, Bais said.

Source: University of Delaware (news : web)

   

• LariAnn - Jun 03, 2009
  • Rank: 2.1 / 5 (7)
  "Phragmites uses this strategy . . .to aggressively conquer... and invade new territory" - what hysterical pseudoscience! The plant has no volition or self-determination, it is just doing what its genes program it to do. The real invader is humanity, who with volition and intent moves plants and animals around the planet, then attempts to blame them when they find a new niche so favorable that they expand their range beyond what humanity thinks is acceptable. So-called invasion biology is more properly categorized with science fiction than science, at least until genuine extraterrestrial alien life forms invade this planet.
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• Ronan - Jun 03, 2009
  • Rank: 5 / 5 (4)
  Whoa, whoa; increased UV radiation due to global warming? Why would overall warmer temperatures increase the intensity of UV-B light? Does the temperature change affect the production or destruction of ozone? Is there a chance anyone knowledgeable about this sort of thing could clarify this for me?
  
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• Birger - Jun 04, 2009
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  Of course the plant has no volition and intent, but natural selection creates organisms that act as if if they did, and thus mimic intent (even humans are to a great deal run by instincts, and thus by the result of selection). In regard to bioinvasion, I couldn't agree more with LariAnn. Unbeleivably, some international economic rules makes it hard for nations to enforce a halt for the import of suspected dangerous species, since it can be considered an intrusion on free trade.... The full economic (and biological) destructive force of invasive species is still not widely appreciated. Not every new species cause damage, but the ones who do are causing destruction valued at tens of billions in the US alone.
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• Doug_Huffman - Jun 04, 2009
  • Rank: 5 / 5 (1)
  Crop the reed for thatching roofs. In an era of failing petroleum supplies for asphalt shingles, do not ignore this burgeoning resource.
  
  Reed has a significant R-value and it sequesters carbon.
  
  Reed is native to many areas of the US and not an 'invasive' species but is aggressively benefiting from climate change.
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• Smellyhat - Jun 04, 2009
  • Rank: 5 / 5 (3)
  ...who else here thought they were gonna read about marijuana?
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