What Is Allelopathy?

By Javier Sánchez, Biologist. February 6, 2024
What Is Allelopathy?

Allelopathy is a complex phenomenon in the natural world where plants release specialized chemicals, known as allelochemicals, that impact the growth, development, and survival of other organisms in their environment. These interactions can be positive, negative, or neutral, influencing various aspects of plant communities and ecosystems. Understanding allelopathy's diverse roles sheds light on intricate natural interactions, with potential applications in various fields.

In the following article by thedailyECO we explain what allelopathy is, exploring its diverse types and ecological significance.

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What is allelopathy?

Allelopathy is a phenomenon in the plant kingdom where one plant species releases chemicals that affect the growth, development, and survival of other plants. These chemicals, called allelochemicals, can have a variety of effects, both positive and negative.

Allelochemicals are a diverse group of compounds, including phenolic acids, terpenes, alkaloids, and volatile organic compounds (VOCs). They can be released from various plant parts, such as roots, leaves, flowers, and fruits.

Allelochemicals can have various effects on other plants, depending on the specific chemicals involved and the target plant species, from the inhibition of germination and to the stimulation of growth.

What is the difference between allelopathy and allelochemicals?

Allelopathy and allelochemicals are two terms that often get intertwined, but they represent distinct aspects of the phenomenon. Allelopathy refers to the broader ecological concept: one plant species impacting another through released chemical compounds.

On the other hand, allelochemicals are the individual molecules released by plants that directly cause the allelopathic effects.

Types of allelopathy

As previously established, allelopathy manifests in diverse interactions that can either positively or negatively affect neighboring organisms. The following classification allows us to categorize and analyze the various strategies plants employ through allelopathy:

Inhibitory Allelopathy

This common strategy involves the release of allelochemicals that suppress or harm the growth and development of other plants. It gives allelopathic plants a competitive advantage by securing vital resources like water and nutrients.

Stimulatory allelopathy

Less frequently observed, this scenario involves allelochemicals that enhance or promote the growth of neighboring plants. This cooperative interaction fosters a mutually beneficial relationship within the ecosystem.

Mutualistic allelopathy

Building upon stimulatory effects, this specialized case forms a reciprocal and flourishing partnership. It highlights the intricate co-evolutionary dance between plants and microorganisms.

Repellent allelopathy

In this defensive strategy, allelochemicals act as chemical deterrents, warding off unwanted herbivores and pests. This allelopathic defense mechanism safeguards the plant from potential damage.

Trap crops

This strategic approach utilizes allelochemicals to lure and capture harmful organisms, protecting valuable crops from their destructive presence. It leverages allelopathy for biological pest control, offering a sustainable alternative to traditional pesticides.

These classifications illustrate the multifaceted nature of allelopathy, showcasing the diverse strategies plants employ to interact with their surrounding environment.

Examples of allelopathy

In this section, we will explore specific examples of allelopathy in action for a deeper understanding of how allelopathy works and its potential implications for various fields.

Inhibitory allelopathy:

  • Black walnut (Juglans nigra): releases juglone, which suppresses nearby plants like tomatoes, peppers, and azaleas by affecting root function and metabolism.

  • Garlic (Allium sativum): releases allicin, inhibiting fungal pathogens beneficial to onions and deterring pests like whiteflies.

  • Eucalyptus trees (Eucalyptus spp.): emit volatile allelochemicals that can hinder the growth of neighboring plants, contributing to their dominance in some ecosystems.

Stimulatory allelopathy:

  • Alder trees (Alnus spp.): Fix nitrogen in the soil through symbiotic bacteria, benefiting nearby plants by increasing nitrogen availability.

  • Cowpeas (Vigna unguiculata): Release compounds that stimulate mycorrhizal fungi, enhancing nutrient uptake for both the cowpea and other surrounding plants.

Mutualistic allelopathy:

  • Corn (Zea mays): Produces exudates that attract beneficial soil bacteria, while the bacteria provide nitrogen and phosphorus to the corn.

  • Legumes (Fabaceae family): Fix nitrogen in the soil through symbiotic bacteria, benefiting neighboring plants that don't fix their own nitrogen.

Repellent allelopathy:

  • Mint (Mentha spp.): Strong scent and volatile menthol deter ants and some insects.

  • Marigold (Tagetes spp.): Releases alpha-terthienyl, a volatile compound that repels whiteflies, nematodes, and some beetles.

Trap crops:

  • Mustard (Brassica nigra): Attracts and traps foliage-feeding caterpillars with its glucosinolates.

  • Marigolds (Tagetes spp.): Attract and trap whiteflies with their sticky trichomes and volatile compounds.

Other interactions:

  • Rice (Oryza sativa): Some cultivars suppress weeds like barnyard grass through allelochemicals, but the exact mechanisms are still being studied.

  • Celery (Apium graveolens): May release volatile allelochemicals suppressing weeds like lamb's quarters while attracting beneficial insects.

You might be interested in this other article that explains which plants repel mosquitoes.

What Is Allelopathy? - Examples of allelopathy

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