Allelopathy
[1] Allelochemicals are a subset of secondary metabolites,[2] which are not directly required for metabolism (i.e. growth, development and reproduction) of the allelopathic organism.
Further confounding the issue, the production of allelochemicals can itself be affected by environmental factors such as nutrient availability, temperature and pH.
[7] Over the next ten years, the term was used by other researchers to describe broader chemical interactions between organisms, and by 1996 the International Allelopathy Society (IAS) defined allelopathy as "Any process involving secondary metabolites produced by plants, algae, bacteria and fungi that influences the growth and development of agriculture and biological systems.
[3] Confusing the issue more, zoologists have borrowed the term to describe chemical interactions between invertebrates like corals and sponges.
[9] In 1832, the Swiss botanist De Candolle suggested that crop plant exudates were responsible for an agriculture problem called soil sickness.
Many have argued that its effects cannot be distinguished from the exploitation competition that occurs when two (or more) organisms attempt to use the same limited resource, to the detriment of one or both.
[3] However, by 1994, D. L. Liu and J. V. Lowett at the Department of Agronomy and Soil Science, University of New England in Armidale, New South Wales, Australia, wrote two papers[10][11] in the Journal of Chemical Ecology that developed methods to separate the allelochemical effects from other competitive effects, using barley plants and inventing a process to examine the allelochemicals directly.
Nilsson at the Swedish University of Agricultural Sciences in Umeå showed in a field study that allelopathy exerted by Empetrum hermaphroditum reduced growth of Scots pine seedlings by ~ 40%, and that below-ground resource competition by E. hermaphroditum accounted for the remaining growth reduction.
However, the use of activated carbon to make inferences about allelopathy has itself been criticized because of the potential for the charcoal to directly affect plant growth by altering nutrient availability.
For example, the discovery that (−)-catechin was purportedly responsible for the allelopathic effects of the invasive weed Centaurea stoebe was greeted with much fanfare after being published in Science in 2003.
[14] One scientist, Dr. Alastair Fitter, was quoted as saying that this study was "so convincing that it will 'now place allelopathy firmly back on center stage.
'"[14] However, many of the key papers associated with these findings were later retracted or majorly corrected, after it was found that they contained fabricated data showing unnaturally high levels of catechin in soils surrounding C.
However, like many allelopathy studies, it was based on artificial lab experiments and unwarranted extrapolations to natural ecosystems.
In 1970, Science published a study where caging the shrubs to exclude rodents and birds allowed grass to grow in the bare zones.
Its success in North American temperate forests may be partly due to its excretion of glucosinolates like sinigrin that can interfere with mutualisms between native tree roots and their mycorrhizal fungi.
[38][39] This research furthers the possibility of using allelochemicals as growth regulators and natural herbicides, to promote sustainable agriculture.
Sheeja (1993) reported the allelopathic interaction of the weeds Chromolaena odorata (Eupatorium odoratum) and Lantana camara on selected major crops.
