Allelopathic mechanisms and experimental methodology

Abstract

Allelopathy is a complex ecological phenomenon, and it has proven notoriously difficult to develop experimental methods that can distinguish the role of both chemical interference and resource competition on plant growth. This paper discusses two promising new methodologies which can be used to study allelopathic interactions in the greenhouse and field. (a) Bioassays in which the density of the susceptible plant species is varied give results contrary to the expected results of resource competition when a toxin is present in the soil. Compared to a control soil, growth reductions will occur at low density but diminish or disappear at high density. Furthermore, individual plant size may actually increase as density increases. These density-dependent phytotoxic effects result from the fact that plants growing at low densities have a larger amount of the toxin available per plant, and therefore suffer greater growth reductions than those in high densities, where each plant receives a proportionately smaller dose of the toxin. (b) Sorbents based on the polymer polydimethyl-siloxane (PDMS) show promise for the measurement of allelochemical fluxes in the rhizosphere. Various forms of PDMS have been demonstrated to pick up increasing amounts of the lipophilic root exudate sorgoleone when buried beneath sorghum-sudangrass hybrid plants. Work is continuing to determine the stability of sorbed compounds, how broad a range of compounds can be effectively trapped by PDMS, and what forms of PDMS are most useful for field studies. © 2008 Springer Science+Business Media LLC.