Allelopathy

Source: Wikipedia, the free encyclopedia.
(Australian) coastal she oak litter completely suppresses germination of understory plants as shown here despite the relative openness of the canopy and ample rainfall (>120 cm/yr) at the location.

Allelopathy is a biological phenomenon by which an organism produces one or more

secondary metabolites,[1]
which are not directly required for metabolism (i.e. growth, development and reproduction) of the allelopathic organism.

Allelopathic interactions are an important factor in determining

invasive plants. For specific examples, see black walnut (Juglans nigra), tree of heaven (Ailanthus altissima), black crowberry (Empetrum nigrum), spotted knapweed (Centaurea stoebe), garlic mustard (Alliaria petiolata), Casuarina/Allocasuarina spp., and nutsedge
.

It can often be difficult in practice to distinguish allelopathy from resource competition. While the former is caused by the addition of a harmful chemical agent to the environment, the latter is caused by the removal of essential nutrients (or water). Often, both mechanisms can act simultaneously. Moreover, some allelochemicals may function by reducing nutrient availability. Further confounding the issue, the production of allelochemicals can itself be affected by environmental factors such as nutrient availability, temperature and pH. Today, most ecologists recognize the existence of allelopathy, however many particular cases remain controversial.

History

The term allelopathy from the

zoologists have borrowed the term to describe chemical interactions between invertebrates like corals and sponges.[2]

Long before the term allelopathy was used, people observed the negative effects that one plant could have on another.

De Candolle suggested that crop plant exudates were responsible for an agriculture problem called soil sickness
.

Allelopathy is not universally accepted among ecologists. Many have argued that its effects cannot be distinguished from the exploitation

Scots pine seedlings by ~ 40%, and that below-ground resource competition by E. hermaphroditum accounted for the remaining growth reduction.[11] For this work she inserted PVC-tubes into the ground to reduce below-ground competition or added charcoal to soil surface to reduce the impact of allelopathy, as well as a treatment combining the two methods. 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.[12]

Some high profile work on allelopathy has been mired in controversy. For example, the discovery that (-)-

retracted or majorly corrected, after it was found that they contained fabricated data showing unnaturally high levels of catechin in soils surrounding C. stoebe.[14][15] [16] Subsequent studies from the original lab have not been able to replicate the results from these retracted studies, nor have most independent studies conducted in other laboratories.[17][18] Thus, it is doubtful whether the levels of (-)-catechin found in soils are high enough to affect competition with neighboring plants. The proposed mechanism of action (acidification of the cytoplasm through oxidative damage) has also been criticized, on the basis that (-)-catechin is actually an antioxidant.[18]

Examples

Garlic mustard

Plants

Many invasive plant species interfere with native plants through allelopathy.[19][20] A famous case of purported allelopathy is in desert shrubs. One of the most widely known early examples was Salvia leucophylla, because it was on the cover of the journal Science in 1964.[21] 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.[22] A detailed history of this story can be found in Halsey 2004.[23]

mycorrhizal fungi.[24][25]

Allelopathy has been shown to play a crucial role in forests, influencing the composition of the vegetation growth, and also provides an explanation for the patterns of forest regeneration.

Spotted knapweed (Centaurea) is considered an invasive plant that also utilizes allelopathy.[29]

Another example of allelopathy is seen in Leucaena leucocephala, known as the miracle tree. This plant contains toxic amino acids that inhibit other plants’ growth but not its own species growth. Different crops react differently to these allelochemicals, so wheat yield decreases, while rice increases in the presence of L. leucocephala.[30][unreliable source?]

Capsaicin is an allelochemical found in many peppers that are cultivated by humans as a spice/food source.[31] It is considered an allelochemical because it is not required for plant growth and survival, but instead deters herbivores and prevents other plants from sprouting in its immediate vicinity.[32][dubious – discuss] Among the plants it has been studied on are grasses, lettuce, and alfalfa, and on average, it will inhibit the growth of these plants by about 50%.[32] Capsaicin has been shown to deter both herbivores and certain parasites’ performance.[33] Herbivores such as caterpillars show decreased development when fed a diet high in capsaicin.

Applications

Further information: Companion planting

Allelochemicals are a useful tool in sustainable farming due to their ability to control weeds.

crabgrass in lawns. Sheeja (1993) reported the allelopathic interaction of the weeds Chromolaena odorata (Eupatorium odoratum) and Lantana camara
on selected major crops.

Many crop cultivars show strong allelopathic properties, of which rice (Oryza sativa) has been most studied.[43][44][45] Rice allelopathy depends on variety and origin: Japonica rice is more allelopathic than Indica and Japonica-Indica hybrid.[citation needed] More recently, critical review on rice allelopathy and the possibility for weed management reported that allelopathic characteristics in rice are quantitatively inherited and several allelopathy-involved traits have been identified.[46] The use of allelochemicals in agriculture provide for a more environmentally friendly approach to weed control, as they do not leave behind residues.[34] Currently used pesticides and herbicides leak into waterways and result in unsafe water qualities. This problem could be eliminated or significantly reduced by using allelochemicals instead of harsh herbicides. The use of cover crops also results in less soil erosion and lessens the need for nitrogen heavy fertilizers.[47]

See also

References

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  14. ^ Brendan Borrell. "NSF investigation of high-profile plant retractions ends in two debarments". Retraction Watch. Retrieved 29 November 2020.
  15. ^ Shannon Palus (3 March 2016). "Sample tampering leads to plant scientist's 7th retraction". Retraction Watch. Retrieved 29 November 2020.
  16. ^ Science, A. A. for the A. of. 2010. Corrections and Clarifications. Science 327:781–781. American Association for the Advancement of Science.
  17. ^ Perry, L. G., G. C. Thelen, W. M. Ridenour, R. M. Callaway, M. W. Paschke, and J. M. Vivanco. 2007. Concentrations of the Allelochemical (+/-)-catechin IN Centaurea maculosa soils. J Chem Ecol 33:2337–2344.
  18. ^ a b Duke, S. O., F. E. Dayan, J. Bajsa, K. M. Meepagala, R. A. Hufbauer, and A. C. Blair. 2009. The case against (–)-catechin involvement in allelopathy of Centaurea stoebe (spotted knapweed). Plant Signaling & Behavior 4:422–424. Taylor & Francis.
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  20. ^ Douglass, Cameron H., Leslie A. Weston, and David Wolfe. 2011. Phytotoxicity and Potential Allelopathy in Pale (Cynanchum rossicum) and Black swallowwort (C. nigrum) Invasive Plant Science and Management 4(1):133-141
  21. ^ Muller, C.H., Muller, W.H. and Haines, B.L. 1964. Volatile growth inhibitors produced by aromatic shrubs. Science 143: 471-473. [1]
  22. ^ Bartholomew, B. 1970. Bare zone between California shrub and grassland communities: The role of animals. Science 170: 1210-1212. [2]
  23. ^ 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. The California Chaparral Institute also offers a PDF-format version of this paper. [3]
  24. ^ 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 [4]
  25. ^ Cipollini, D. 2016. A review of garlic mustard (Alliaria petiolata, Brassicaceae) as an allelopathic plant. tbot 143:339–348. Torrey Botanical Society.
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  39. ^ Chen, X.H., Hu, F., Kong, C.H., 2008. Varietal improvement in rice allelopathy. Allelopathy Journal, 22: 379-384.
  40. ^ Kaiser, Jerry (January 2016). "Allelopathy and Cover Crops" (PDF). nrcs.usda.gov. Retrieved 8 June 2022.
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Further reading

External links

Look up allelopathy in Wiktionary, the free dictionary.
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