Monday, January 21, 2013

Ashland team challenges hypothesis for the success of wetland invader

The common reed, Phragmites australis, is a serious invasive weed in North American wetlands and one of the most serious invasive plants in the world.  According to a recent hypothesis, the roots of this plant release a toxic chemical, gallic acid, which is responsible for its success as an invader.  However, a team of Ashland faculty and students has found no evidence to support this hypothesis in a study that has just been published in the Journal of Chemical Ecology.  The paper, titled “Evidence does not support a role for gallic acid in Phragmites australis invasion success,” appears in a special issue of the journal on allelochemical interactions in croplands and natural settings. 

Mei Li, a 2013 Chemistry graduate, conducted research with Dr. Jeff Weidenhamer showing that contrary to other published reports, gallic acid breaks down very rapidly in Phragmites soils.  She was also unable to find evidence for gallic acid in Phragmites soil collected in North Carolina by Dr. Mason Posner and students in his Marine Biology class.  Mei, working with Dr. Weidenhamer and Dr. Robert Bergosh, then undertook an investigation of the chemistry of Phragmites plants from several populations in North Carolina and Ohio.  She successfully isolated one of the major components of extracts of the plant, and this compound was identified with the aid of the Chemistry Department’s new high field NMR spectrometer.  Further work established that Phragmites plants contain only trace amounts of gallic acid, in contrast to previous reports that the roots contain and release very high concentrations of this compound.  Junior biology major Joshua Allman (pictured above with Dr. Posner) worked to establish that all of the plant populations sampled were of the invasive genotype previously reported to contain high levels of gallic acid. 

Students in AU's Marine Biology course collecting some
of the samples used in this study.
 Dr. Jeff Weidenhamer, lead author of the study, began studying allelopathy – interactions among plants that are mediated by toxic chemicals – in graduate school.  Much of his research has been devoted to the development of new methods to improve the understanding of these chemical interactions.  One of the plants that he has previously studied from the Florida scrub community appears to produce chemicals that inhibit the germination and growth of grasses.  In that case, he implicated degradation products of gallic acid and another compound as the cause of these effects.  In this study, he notes that while the occurrence of high concentrations of gallic acid in some populations of P. australis can’t be ruled out, the trace concentrations found in this study show that the release of this compound cannot be a primary, general explanation for the success of this plant in wetlands.  He concludes, “As we tell our students, a key point of the scientific method is that research ought to be repeatable.  It was a great experience for them to participate in and help design experiments to test these recent findings.”  

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