Аллелопатия

Аллелопатия (от греч. allēlōn — взаимно и páthos — страдание), влияние растений друг на друга в результате выделения ими различных веществ. Известны 4 группы таких веществ. Вещества двух групп образуются микроорганизмами; это — антибиотики, подавляющие жизнедеятельность других микроорганизмов, и маразмины (вещества завядания), действующие на высшие растения. Вещества двух других групп выделяются высшими растениями — это фитонциды, подавляющие жизнедеятельность микроорганизмов, и колины, тормозящие развитие высших растений. Иногда наблюдается положительное влияние растений друг на друга, что особенно важно в агрофитоценозах. Явление А. необходимо учитывать при возделывании с.-х. растений (севообороты, подбор культур для смешанных посевов и др.).

Лит.: Гродзинский А. М., Аллелопатия в жизни растений и их сообществ, К., 1965; Физиолого-биохимические основы взаимного влияния растений в фитоценозе М., 1966.

Аллелопа́тия (от др.-греч. ἀλλήλων (allelon) — взаимно и πάθος (pathos) — страдание), свойство растений и микроорганизмов выделять органические соединения, которые тормозят развитие других растений или микроорганизмов.

Различают четыре группы веществ, ответственных за А.:

• антибиотики — выделяются микроорганизмами, служат для подавления жизнедеятельности других микроорганизмов;

• маразмины — выделяются микроорганизмами, служат для подавления жизнедеятельности высших растений;

• фитонциды — выделяются высшими растениями, служат для подавления жизнедеятельности микроорганизмов;

• колины — выделяются высшими растениями, служат для подавления жизнедеятельности других высших растений.

А. можно рассматривать как форму экологической конкуренции между организмами в фитоценозах.

В практическом плане изучение А. имеет важное сельскохозяйственное значение. Кроме того, это явление следует учитывать при составлении букетов.

Термин «А.» используется также при страховании — так называют взаимное влияние перевозимых растительных грузов. А. с точки зрения страхования является фактором повышенного риска.

Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms. Allelochemicals are a subset of secondary metabolites,  which are not required for metabolism (i.e. growth, development and reproduction) of the allelopathic organism. Allelochemicals with negative allelopathic effects are an important part of plant defense against herbivory. 

Allelopathy is characteristic of certain plants, algae, bacteria, coral, and fungi. Allelopathic interactions are an important factor in determining species distribution and abundance within plant communities, and are also thought to be important in the success of manyinvasive plants. For specific examples, see Spotted Knapweed (Centaurea maculosa), Garlic Mustard (Alliaria petiolata), and Nutsedge.

The process by which a plant acquires more of the available resources (such as nutrients, water or light) from the environment without any chemical action on the surrounding plants is called resource competition. This process is not negative allelopathy, although both processes can act together to enhance the survival rate of the plant species.

The term allelopathy, from the Greek-derived compounds allelo- and -pathy (meaning "mutual harm" or "suffering"), was first used in 1937 by the Austrian professor Hans Molisch in the book Der Einfluss einer Pflanze auf die andere - Allelopathie (The Effect of Plants on Each Other) published in German.  He used the term to describe biochemical interactions that inhibit the growth of neighbouring plants, by another plant.  In 1971, Whittaker and Feeny published a study in the journal Science, which defined allelochemicals as all chemical interactions among organisms.  In 1984, Elroy Leon Rice in his monograph on allelopathy enlarged the definition to include all direct positive or negative effects of a plant on another plant or on micro-organisms by the liberation of biochemicals into the natural environment.  Over the next ten years, the term was used by other researchers to describe broader chemical interactions between organisms, and by 1996 the International Homeopathy Society 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."  In more recent times, plant researchers have begun to switch back to the original definition of substances that are produced by one plant that inhibit another plant.  Confusing the issue more, zoologists have borrowed the term to describe chemical interactions betweeninvertebrates like corals and sponges. 

Long before the term allelopathy was used, people observed the negative effects that one plant could have on another. Theophrastus, who lived around 300 BC noticed the inhibitory effects of pigweedon alfalfa. In China around the first century AD, the author of Shennong Ben Cao Jing described 267 plants that had pesticidal abilities, including those with allelopathic effects. In 1832, the Swiss botanist De Candolle suggested that crop plant exudates were responsible for an agriculture problem called soil sickness.

Allelopathy has not been universally accepted among ecologists, and up to the early part of this century many ecologists argued that the effects of competition could not be distinguished from so called allelopathy. Competition is a negative effect which presents when two or more organisms attempt to directly use the same resource. Allelopathy, on the other hand differs by indirectly affecting other organisms after the input of substances into the environment. In the 1970s, great effort went into distinguishing competitive and allelopathic effects by some researchers, while in the 1990s others argued that the effects were often interdependent and could not readily be distinguished. 

The possible application of allelopathy in agriculture is the subject of much research.  Current research is focused on the effects of weeds on crops, crops on weeds, and crops on crops.  This research furthers the possibility of using allelochemicals as growth regulators and natural herbicides, to promote sustainable agriculture.  A number of such allelochemicals are commercially available or in the process of large-scale manufacture. For example, Leptospermone is a purported thermochemical in lemon bottlebrush (Callistemon citrinus). Although it was found to be too weak as a commercial herbicide, a chemical analog of it, mesotrione (tradename Callisto), was found to be effective.  It is sold to control broadleaf weeds in corn but also seems to be an effective control forcrabgrass 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.  Rice allelopathy depends on variety and origin: Japonica rice is more allelopathic than Indica and Japonica-Indica hybrid. 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. 

Many invasive plant species interfere with native plants through allelopathy.  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.  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.  A detailed history of this story can be found in Halsey 2004. 

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. The black walnut (Juglans nigra) produces the allelochemical juglone, which affects some species greatly while others not at all. Eucalyptus leaf litter and root exudates are allelopathic for certain soil microbes and plant species. The tree of heaven, Ailanthus altissima, produces allelochemicals in its roots that inhibit the growth of many plants. The pace of evaluating allelochemicals released by higher plants in nature has greatly accelerated, with promising results in field screening. 

Garlic mustard is an invasive plant species in North American temperate forests. Its success may be partly due to its excretion of an unidentified allelochemical that interferes with mutualisms between native tree roots and their mycorrhizal fungi. 

A study of Kochia scoparia in northern Montana by two high school students  showed that when Kochia precedes spring wheat (Triticum aestivum), it reduces the spring wheat's growth. Effects included delayed emergence, decreased rate of growth, decreased final height and decreased average vegetative dry weight of spring wheat plants.  A larger study later showed that Kochia seems to exhibit allelopathy on various crops in northern Montana. 

Corn gluten meal (CGM) is a natural preemergence weed control used in turfgrass, which reduces germination of many broadleaf and grass weeds.