Allelopathy and its Influence on the Distribution of Plants in an Illinois Old-Field

SUMMARY (1) A whole-community investigation of allelopathy in an old-field in Illinois was undertaken, by comparing bioassay results with association patterns in the field. (2) The seven most abundant species in the field were tested upon each other in nine commonly-used bioassays. Eight of the nine bioassays gave many cases of statistically significant inhibition, and strong phytotoxicity was exhibited by species which have not previously been suspected of being allelopathic and which show no readily-observable signs of allelopathy in the field. (3) Autotoxicity was found to be as severe as allotoxicity, indicating that the species have not evolved resistance to their own inhibitors. (4) When the distribution patterns of species in the field were statistically compared with the results of each of the bioassays in turn, no significant correlations were found. (5) It was concluded that the types of allelopathy which were tested by these bioassays were not demonstrably effective under field conditions, that perhaps any species can be shown to have allelopathic properties in bioassays, and that bioassays may, for many communities, have no ecological meaning.