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.
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.
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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 |
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 |
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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. |
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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.
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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 (
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.
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:
For Reprints: jweiden@ashland.edu
Professional Societies:
International
Society of Chemical Ecology
Phytochemical Society of North America
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