Chemical Ecology Research - J Weidenhamer

Chemical Ecology is the study of the role of chemical substances in mediating relationships between organisms.  My particular interest is in the phenomenon of allelopathy, or chemical interference among higher plants.

Research on Methods for Investigation of Allelopathy:
It has long been suspected that toxic chemicals released by plants into the soil may function as natural herbicides to inhibit the growth of neighboring plants.  If this is the case, such chemicals could influence important ecological processes such as successional changes in plant communities over time, and nutrient cycles.  Recently, it has been proposed that the success of certain invasive plants might be due to the chemical toxins they produce.  One of the major barriers to evaluating these ideas has been the difficulty of analyzing the release of these chemicals in the soil.  My lab’s recent work focuses on the development and application of new polymer-based materials such as polydimethylsiloxanes that can trap these chemicals as they are released in the soil, allowing these toxins to be isolated and measured.  This research will provide an inexpensive tool for other scientists to use in investigating these problems.  This work has been funded by the National Science Foundation, Division of Ecological Biology.

A major outcome of this research has been the development of a new technique for analysis of root exudates which we call silicone tube micro extraction.  Silicone microtubing is placed directly in soil, and lipophilic root exudates are eluted from the tubing for HPLC analysis using an organic solvent such as methanol.  The photo below was taken by my colleague Rod Michael, and shows microtubing placed over roots of the marigold Tagetes erecta L. 

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The broader implications of this project are two-fold.  First, understanding how chemicals released by plants do or do not function as natural herbicides may suggest new ways to manage and control certain invasive species that have caused widespread damage to natural and managed land.  In agriculture, such chemicals might be used as more ecologically-sound replacements for synthetic herbicides. 

 

Summer06

Solar

Loi

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Boes

 

Students working on this project in Summer 2006 were (clockwise from center top) Marissa Solar, Rebecca Loi, Philip Boes and David Wilcox

 

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At the St Louis Arch

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At the Missouri Botanical Garden

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My research group with posters at the meeting of the Phytochemical Society of North America – July 2007, St. Louis

 

Students who worked on this project during Summer 2007 were (left to right in top left photo) Jamie Yost, David Wilcox, Rebecca Loi, and Philip Boes. 

 

 

 

 

 

 

 

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The Weidenhamers, Mohneys, and undergraduate student researchers Jessica

LaMoreaux, Tricia Matz, and Kelly Harrison enjoying the Baltimore inner harbor.

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Above: Kelly Harrison standing with me by her poster

at the Aug. 2009 Meeting of the Phytochemical Society

of North America in Baltimore. 

 

Below: Tricia Matz and Jessical LaMoreaux stand with

me and colleague Brian Mohney by their poster on

silicone tube microextraction.

 

 

During the summer of 2009, three students worked on this project with me and colleague Brian Mohney.  The students presented results of their work in two posters at the meeting of the Phytochemical Society of North America at Towson State University.

In addition to my work on rhizosphere analysis, a significant portion of my previous research has been in the area of greenhouse and field methods for studies of chemical interference between plants.  It has proven extraordinarily difficult to demonstrate that the inhibition of plant growth observed in the field or greenhouse are due to toxic chemicals being released by a neighbor, and not due to effects such as competition for moisture and nutrients.  We have found that phytotoxic effects are density-dependent at low plant densities, there is more of the toxin available per plant and therefore a greater toxic effect than is observed at higher densities.  This sort of response is inconsistent with resource competition.

Pertinent papers:

Mohney, B., Matz, T.*, LaMoreaux, J.*, Wilcox, D.*, Gimsing, A., Mayer, P. and J. Weidenhamer.  2009.  In situ silicone tube microextraction:  A new method for undisturbed sampling of root-exuded thiophenes from marigold (Tagetes erecta L.) in soil.   In press, Journal of Chemical Ecology 35(11).  DOI: 10.1007/s10886-009-9711-8

 

Weidenhamer, J., Boes, P.* and D. Wilcox.* 2009.  Solid-phase root zone extraction (SPRE):  A new methodology for measurement of allelochemical dynamics in soil.  Plant and Soil, 322: 177-186.  DOI: 10.1007/s11104-009-9905-4.

 

Dayan , F., Howell, J. and Weidenhamer, J.  2009. Dynamic root exudation of sorgoleone and its in planta mechanism of action.  Journal of Experimental Botany, 60, 2107–2117.

 

Loi, R.*, Solar, M. and J. Weidenhamer.  2007.  Solid phase microextraction method for in vivo measurement of allelochemical uptake.  Journal of Chemical Ecology, 34:70-75.

 

Weidenhamer, J.  2005.  Biomimetic measurement of allelochemical dynamics in the rhizosphere.  Journal of Chemical Ecology.   31(2): 221-236.

 

* identifies undergraduate co-authors.

Research on Allelopathic Effects of Florida Scrub Perennials:
Much of my work has been done on perennial shrubs of the Florida scrub community.   Younger sites are dominated by perennial shrubs such as the Florida rosemary (Ceratiola ericoides) shown on my home page, and other locally abundant shrubs such as Calamintha ashei, Conradina canescens, Chrysoma pauciflosculosa, and Polygonella myriophylla; while mature scrubs are dominated by sand pine (Pinus clausa) and oaks (Quercus chapmanii , Q. myrtifolia and Q. geminata).  The scrub contains little herbaceous understory, and several workers have been investigating the hypothesis that allelopathic interference by fire-sensitive shrubs of the scrub community deters the invasion of fire-prone grasses and pines from the neighboring sandhill community.
 

 

polygonella

At this site, Polygonella myriophylla shrubs border an abandoned citrus field that has been taken over by bahiagrass, Paspalum notatum.  The bare zone is approximately 1 m wide. Polygonella myriophylla produces a number of phenolic compounds, including very high concentrations of hydroquinone derivatives, which appear to play a role in the allelopathic activity observed in laboratory and field experiments.  Ongoing work shows that microorganisms play an important role in the degradation of these compounds in soil.

 

                                                                             

Pertinent papers:

 

Weidenhamer, J. and J. Romeo.  2005.  “Allelopathy as a mechanism for resisting invasion: The case of Polygonella myriophylla.”  Pp. 167-177 In:  (Inderjit, ed.) Invasive Plants: Ecological and Agricultural Aspects (Switzerland: Birkhauser-Verlag AG).

 

Weidenhamer, J and J. Romeo.  2004.  Allelochemicals of polygonella myriophylla: chemistry and soil degradation.  Journal of Chemical Ecology 30(5): 1067-1082.

Weidenhamer, J., M.A. Menelaou, F.A. Macias, N.H. Fischer, D.R. Richardson and G.B. Williamson. 1994. Allelopathic potential of menthofuran monoterpenes from Calamintha ashei. Journal of Chemical Ecology, 20(12):3345-3359.

Fischer, N.H., G.B. Williamson, J. Weidenhamer and D.R. Richardson. 1994. In search of allelopathy in the Florida scrub: The role of terpenoids. Journal of Chemical Ecology, 20(6):1355-1380.

Weidenhamer, J., F. Macias, N. Fischer and G. Williamson.  1993.  Just how insoluble are monoterpenes?  Journal of Chemical Ecology, 19(8):1827-1835.

Weidenhamer, J. and J. Romeo. 1989. Allelopathic properties of Polygonella myriophylla: Field evidence and bioassays. Journal of Chemical Ecology, 15(7):1957-1970.

Some Scrub Links:

Archbold Biological Station

For Reprints:     jweiden@ashland.edu

Professional Societies:

International Society of Chemical Ecology
Phytochemical Society of North America

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