Research Interests - 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 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
is funded by the National Science Foundation, Division of Ecological Biology.
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
Link to Article about Summer 2006 Student Research
In addition to my currently funded 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:
Weidenhamer, J., D. Hartnett and J. Romeo. 1989. Density-dependent phytotoxicity: Distinguishing resource competition and allelopathic interference in plants. Journal of Applied Ecology, 26(2):613-624.
Williamson, G. and J. Weidenhamer. 1990. Bacterial degradation of juglone: Evidence against Allelopathy? Journal of Chemical Ecology, 16(5):1739-1741.
Thijs, H.*, J.D. Weidenhamer and J.R. Shann. 1994. The effect of phytotoxins on competitive outcome in a model system. Ecology, 75(7):1959-1964.
Weidenhamer, J.D. 1996. Distinguishing resource competition and chemical interference: Overcoming the methodological impasse. Agronomy Journal, 88(6):866-875.
Romeo, J.T. and J.D. Weidenhamer. 1998. Bioassays for Allelopathy in Terrestrial Plants. In Methods of Chemical Ecology, Volume 2: Bioassay Methods. Expected publication date: March 1998.
Weidenhamer, J. 2005.
Biomimetic measurement of allelochemical dynamics in the
rhizosphere. Journal
of Chemical Ecology. 31(2):
221-236.
Weidenhamer, J.
2006. Distinguishing allelopathy
from resource competition: The role of density.
Pp. 85-103 in Allelopathy: A
physiological process with ecological implications, edited by Manuel Reigosa, Nuria Pedrol and Luís González, published by Springer. (Invited review chapter).
Research on Allelopathic Effects of
Much of my work has been done on perennial shrubs of the
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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, that 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.
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Pertinent papers:
Weidenhamer, J. and J. Romeo. 1989. Allelopathic properties of Polygonella myriophylla: Field evidence and bioassays. Journal of Chemical Ecology, 15(7):1957-1970.
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., M.A. Menelaou,
F.A.
Weidenhamer,
J and J. Romeo. 2004. Allelochemicals of polygonella
myriophylla: chemistry and soil degradation. Journal
of Chemical Ecology 30(5):
1067-1082.
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 (
Some Scrub Links:
For Reprints: jweiden@ashland.edu
Professional Societies:
International Society of Chemical Ecology
Phytochemical
Society of North America
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