Casuarina equisetifolia litter completely suppresses germination of understory plants as shown here despite the relative openess of the canopy and ample rainfall (>120 cm/yr) at the location

The term allelopathy denotes the production of specific biomolecules by one plant that can induce suffering in, or give benefit to, another plant. However, it is most commonly used in the former sense - an interaction in which one plant causes suffering to another plant. Image File history File linksMetadata Download high resolution version (1600x1200, 443 KB)Photograph of ground beneath a forest of Casuarina equisetifolia (ironwood) trees showing allelopathy. ... Image File history File linksMetadata Download high resolution version (1600x1200, 443 KB)Photograph of ground beneath a forest of Casuarina equisetifolia (ironwood) trees showing allelopathy. ... Selected species Casuarina cunninghamiana Casuarina equisetifolia Casuarina glauca Casuarina is a genus of shrubs and trees in the Family Casuarinaceae, native to Australia and islands of the Pacific. ...

Conceptually, biomolecules (specifically termed allelochemicals) produced by a plant are released into the environment and subsequently influence the growth and development of neighbouring plants. It is important to keep in mind that allelopathy involves the addition of a chemical compound or compounds (secondary metabolites) into the environment, while "competition" involves the removal or reduction of some factor or factors in the environment (such as nutrients, water, or light).

Although allelopathic science is a relatively new field of study, there exists convincing evidence that allelopathic interactions between plants play a crucial role in both natural and manipulated ecosystems. These interactions are undoubtedly an important factor in determining species distribution and abundance within some plant communities. Allelopathic interactions are also thought to be an important factor in the success of many invasive plants. For specific examples, see Spotted Knapweed and Nutsedge. In biology, a species is one of the basic units of biodiversity. ... A biocoenosis (alternatively, biocoenose or biocenose), termed by Karl Möbius in 1877, describes all the interacting organisms living together in a specific habitat (or biotope). ... It has been suggested that this article or section be merged into Invasive species. ... Binomial name Cyperus rotundus L. Cyperus rotundus (coco-grass, nut sedge, nut-grass, purple nut sedge, red nut sedge) is a pantropic species of sedge (Cyperaceae) that has spread-out to become a world-wide introduced weed. ...

Mechanisms of action

There are hundreds of secondary metabolites in the plant kingdom, and many are known to be phytotoxic (Einhellig, 2002). Allelopathic effects of these compounds are often observed to occur early in the life cycle, causing inhibition of seed germination and/or seedling growth. The compounds exhibit a wide range of mechanisms of action, from affects on DNA (alkaloids), photosynthetic and mitochondrial function (quinones), phytohormone activity, ion uptake, and water balance (phenolics). Interpretations of mechanisms of action are complicated by the fact that individual compounds can have multiple phytotoxic effects (Einhellig, 2002). A metabolite is the product of metabolism. ... A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction. ... A ripe red jalapeno cut open to show the seeds For other uses, see Seed (disambiguation). ... Sunflower seedlings, just three days after germination Germination is the process where growth emerges from a resting stage. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ... Diagram of Ephedrine An alkaloid is a nitrogenous organic molecule that has a pharmacological effect on humans and animals. ... The leaf is the primary site of photosynthesis in plants. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... An ion is an atom or group of atoms that normally are electrically neutral and achieve their status as an ion by loss or addition of one or more electrons. ... Water is a tasteless, odourless substance that is essential to all known forms of life and is known as the universal solvent. ...

Demonstrating allelopathy in nature

The vast majority of allelopathy research attempts to focus on direct negative plant-plant interactions caused by allelochemicals. One of the greatest challenges of this approach is showing that the effect is direct, since allelochemicals can have indirect effects on plant species through interaction with biotic (e.g. mycorrhizae) and/or abiotic soil factors (e.g. nutrient availability; anon., 2002). In terrestrial systems, the soil plays an important role as the matrix through which potential allelochemicals pass. Both abiotic and microbial decomposition will have significant effects on the concentration of allelochemicals reaching other plants. A mycorrhiza (typically seen in the plural form mycorrhizae meaning fungus roots) is a distinct type of root symbiosis in which individual hyphae extending from the mycelium of a fungus colonize the roots of a host plant. ... Loess field in Germany Soil horizons are formed by combined biological, chemical and physical alterations. ... A nutrient is either element or compound necessary for or contributing to an organisms metabolism, growth, or other functioning. ...

Proving that allelopathy is occurring is difficult for the reason that it is difficult to separate the effects of allelopathy from those due to resource competition (e.g., for space, light, water, nutrients or CO₂). Controlled greenhouse studies that allow for examination of a single independently varying factor may be of little interest since the factors do not vary independently in nature. Willis (1985) required that six criteria be met, and even when maximally relaxed to just three, proving allelopathy is rarely if ever accomplished (Blum et al., 1999). Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... A greenhouse in Saint Paul, Minnesota. ...

1. pattern of inhibition of one species by another
2. putative aggressor must produce a toxin
3. known mode of release of this toxin
4. toxin transport or accumulation in the environment
5. afflicted plant have means of uptake of toxin
6. observed pattern of inhibition cannot be solely explained by physical competition or other biotic factors

Role of plant stress

Allelopathy also interacts with plant stress, because stressed source plants often release a greater array and concentration of allelochemicals, and stressed target plants may be more susceptible to allelochemicals (Reigosa et al., 2002). Measurement of the effects of allelochemicals along stressor gradients should help to elucidate the relationship between allelopathy and stress.

Examples of allelopathy

One of the most studied aspects of allelopathy is the role of allelopathy in agriculture. Current research is focused on the effects of weeds on crops, crops on weeds (Pheng et al. 1999), and crops on crops. This research furthers the possibility of using allelochemicals as growth regulators and natural pesticides (a number of them are either commercially available or in the process of large-scale manufacture) to promote sustainable agriculture. Leptospermone is a purported allelochemical in lemon bottlebrush (Callistemon citrinus). It was investigated as a possible commercial herbicide but was found to be too weak. However, a chemical analog of leptospermone was found to be an effective herbicide. The analog is mesotrione, tradename Callisto.^[1] It is sold to control broadleaf weeds in corn but also seems to be an effective control for crabgrass in lawns.

One of the most famous cases of purported allelopathy is in desert shrubs. Salvia leucophylla was one of the most widely known early examples because it was on the cover of the journal Science in 1964^[2] Bare zones around the shrubs were hypothesized to be caused by volatile terpenes emitted by the shrubs. 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.^[3] A detailed history of this interesting story can be found in Halsey 2004.^[4] Erg Chebbi, Morocco In geography, a desert is a landscape form or region that receives very little precipitation. ... A broom shrub in flower A shrub or bush is a horticultural rather than strictly botanical category of woody plant, distinguished from a tree by its multiple stems and lower height, usually less than 6 m tall. ... Binomial name Salvia leucophylla Greene Salvia leucophylla (Purple Sage) is an aromatic sage native to the southern coast of California and Baja California, with a range stretching from Santa Maria southward, at 50–800 m altitude. ... Science is the journal of the American Association for the Advancement of Science (AAAS). ...

In other studies allelopathy has been demonstrated to play a crucial role in forests, influencing the composition of the vegetation growth, while also providing an explanation for the patterns of forest regeneration. The black walnut (Juglans nigra) produces juglone, an allelopathic substance that interferes with the growth of other plants. Juglone is somewhat selective, with certain species greatly affected by it and others not affected at all. Eucalyptus leaf litter and root exudates are allelopathic for certain soil microbes and plant species. The tree of heaven, (Ailanthus altissima) produces allelopathic substances in its roots that inhibit the growth of many plants. Furthermore, the trends of evaluating allelochemicals release from higher plants in natures are much concentrated and showed a promising results of field screening.Khanh and Xuan ^[5] Binomial name Juglans nigra L. The Black Walnut or American Walnut (Juglans nigra L.) is a native of eastern North America, where it grows, mostly alongside rivers, from southern Ontario, Canada west to southeast South Dakota, south to Georgia and southwest to central Texas. ... Juglone is an aromatic organic compound with the molecular formula C10H6O3. ... Species About 700; see the List of Eucalyptus species Eucalyptus is a diverse genus of trees (and a few shrubs), the members of which dominate the tree flora of Australia. ... Species Ailanthus altissima Ailanthus excelsa Ailanthus giraldii Ailanthus malabarica Ailanthus triphysa Ailanthus vilmoriniana Ailanthus (derived from ailanto, an Amboine word probably meaning tree of the gods or tree of heaven) is a genus of 6-10 species of trees belonging to the family Simaroubaceae, in the order Rutales. ...

Garlic mustard is an invasive plant in North American temperate forests. Its success may be partly due to its excretion of a not yet identified allelochemical that interferes with mutualisms between native tree roots and their mycorrhizal fungi.^[6] Binomial name Alliaria petiolata (M.Bieb. ... Ant-aphid mutualism: the aphids are protected against predators by the ants who cultivate the aphids for their secretions of honeydew, a food source. ... Millions of years ago, trees, flowers and grasses faced many natural stresses, such as low soil fertility, drought and temperature extremes. ...

A study of kochia (Kochia scoparia) in North Toole County (NTC), Montana by two high school students showed that when kochia precedes spring wheat (Triticum aestivum), it reduces the spring wheat's performance. Among these effects are delayed emergence, decreased rate of growth, decreased final height, and decreased average vegetative dry weight of spring wheat plants. ^[7] This small study was followed by another which further showed that kochia does seem to exhibit allelopathic effects on various crops grown in northern Montana. ^[8] For their work in the area Overcast & Cox were awards a first place team prize at the International Science and Engineering Fair ISEF in 2001. A science fair is (generally) a competition where contestants create a personal project related to science or some scientific phenomenon. ...

References

1. ^ Cornes, D. 2005. Callisto: a very successful maize herbicide inspired by allelochemistry. Proceedings of the Fourth World Congress on Allelopathy [1]
2. ^ Muller, C.H., Muller, W.H. and Haines, B.L. 1964. Volatile growth inhibitors produced by aromatic shrubs. Science 143: 471-473. [2]
3. ^ Bartholomew, B. 1970. Bare zone between California shrub and grassland communities: The role of animals. Science 170: 1210-1212. [3]
4. ^ Halsey, R.W. 2004. In search of allelopathy: An eco-historical view of the investigation of chemical inhibition in California coastal sage scrub and chamise chaparral. Journal of the Torrey Botanical Society 131: 343-367. A pdf copy of this paper can be obtained from the California Chaparral Field Institute. [4]
5. ^ Khanh, T.D, Hong, N.H., Xuan, T.D. Chung, I.M. 2005.Paddy weed control by medical and leguminous plants from Southeast Asia .Crop Protection [doi:10.1016/j.cropro.2004.09.020]
6. ^ Stinson, K.A., Campbell, S.A., Powell, J.R., Wolfe, B.E., Callaway, R.M., Thelen, G.C., Hallett, S.G., Prati, D., and Klironomos, J.N. 2006. Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms. PLoS Biology [5]
7. ^ M.C. Overcast, J.J. Brimhall. 2000. Allelopathic Effects of Selected Weed Exudates on Germination and Early Growth of Triticum aestivum in Northern Toole County, Montana. [6]
8. ^ M.C. Overcast, D.R. Cox. 2001. Effects of Allelochemicals Produced by Kochia scoparia on Selected Crops Grown in North Toole County (NTC), Montana.

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