Study Finds Plants Detect Neighbors' Growth Rate Through Chemical Scents

A recent study has demonstrated that plants can "smell" how fast neighboring plants are growing by detecting chemical scents they emit into the air. Based on these chemical signals, plants then modify their growth or defensive strategies.

The study explains that these airborne chemical scents are known as "volatile organic compounds." These compounds are familiar to humans as they produce the pleasant fragrances found in flowers and are used in perfumes, cosmetics, and food products. However, their primary role in nature is communication: plants use them to interact with insects, animals, and even other plants.

In simple terms, plants can "interpret" the intentions of their neighbors through these scents. If a plant detects the scent of a fast-growing neighbor, it accelerates its own growth to compete for light and water. Conversely, if it senses a slow-growing neighbor's scent, it directs energy toward strengthening defenses against insects and herbivores instead.

Until recently, scientists believed that plants employed these scents only in response to threats, such as sending alarm signals when a plant is damaged. However, a new study published in the Journal of Experimental Botany reveals that healthy, undamaged plants also continuously communicate in what Dr. Vilmer Ninkovich from the Swedish University of Agricultural Sciences describes as an "ongoing conversation among neighbors."

To verify this, researchers conducted experiments on three barley strains—one slow-growing (Fairytale), one medium-growing (Luhkas), and one fast-growing (Salome). They exposed the slow and fast strains to the scents of all three strains and observed the results after 25 days.

The findings were clear: plants exposed to the scent of a fast-growing neighbor exhibited greater growth, while those exposed to the scent of a slow-growing neighbor showed reduced growth.

Crucially, this change occurred across all plant parts—leaves, stems, and roots—indicating a complete shift in growth strategy rather than merely reallocating resources within the plant.

Genetic analysis revealed that exposure to the slow-growing plant's scent activated defense-related genes that protect against insects and suppressed growth-related genes. In contrast, exposure to the fast-growing plant's scent produced the opposite effect, prioritizing growth over defense readiness.

The researchers precisely identified the chemical compounds responsible for these signals, including linalool, found in lavender, and octanal, present in citrus fruits.

Scientists believe this phenomenon likely exists in most plant species after millions of years of evolution, although the strength of the response and specific compounds involved may vary between plants. This discovery could have significant agricultural applications, such as enhancing understanding of crop behavior when planted together, potentially aiding farmers in optimizing crop production.