How barley plants use VOCs to anticipate neighbours’ growth

A field can seem still at first glance: leaves flutter in the breeze, stems lean towards the sun, and roots expand unseen below the surface. Yet above ground, an unseen exchange is taking place.

As part of their ordinary day-to-day biology, plants emit tiny chemical compounds into the air. Nearby plants can detect some of these compounds and alter how they behave.

For many years, scientists have understood that plants can send out warning signals when insects attack. A new study from the Swedish University of Agricultural Sciences points to something broader: even healthy plants may use airborne cues to interpret how their neighbours are growing.

In other words, plants may not wait until competition is obvious. They may start preparing for it beforehand.

Plants communicate beyond danger

Plant-to-plant communication is often described as an emergency response: one plant is attacked, it releases chemicals, and surrounding plants ready their defences.

That mechanism is real. However, this research focused on a different category of message.

Healthy plants continuously give off volatile organic compounds, or VOCs - airborne chemicals that drift from one plant to another. Importantly, these emissions are part of normal plant function, not solely a reaction to harm.

Everyday plant signals

The researchers set out to test whether these routine chemical emissions have consequences for neighbouring plants.

“Healthy non-damaged plants are constantly releasing their own chemical ‘fingerprint’ into the air, and their neighbors actively read these signals to adjust not only their defenses, but their entire growth strategy,” said Dr. Velemir Ninkovic, lead author of the study.

“This is like a continuous conversation between neighbors, and the finding that these background VOCs can reshape growth and gene activity opens up a new dimension in how we understand plant communication.”

A simple barley test

To explore the idea, the team worked with three barley cultivars: Fairytale, Luhkas, and Salome.

These varieties were chosen because their growth rates differ. Fairytale is slow growing, Salome grows quickly, and Luhkas falls between the two.

Plants were placed inside transparent chambers designed so that air - and therefore chemical signals - could pass from one to another.

At the same time, the plants were kept physically separate: they could not touch, share soil, or interact through their roots.

This design allowed the researchers to isolate a single factor: what changes when a plant is exposed only to another plant’s airborne chemicals?

Neighbor scents changed plant growth

The growth responses were clear. When the slow-growing Fairytale plants were exposed to VOCs from the fast-growing Salome, Fairytale increased its growth and produced more biomass.

The reverse pattern also appeared. When Salome received VOCs from the slow-growing Fairytale, Salome’s growth decreased.

Luhkas, as the intermediate grower, produced milder effects. And when plants were exposed to signals from a cultivar with a similar growth speed, the impact was minimal.

Together, these patterns indicate the plants were not responding at random; they appeared to adjust according to the type of neighbour nearby.

Growth has costs

Plants operate with finite energy. That energy can be used to increase size, or it can be devoted to defence against insects, disease, and environmental stress.

They cannot maximise every function simultaneously. Rapidly growing plants commonly prioritise speed and size.

Slower-growing plants, by contrast, often allocate more resources to defence.

Plants predict competition

The findings indicate that plants may use scent-based information to assess what sort of neighbour they are facing.

If the nearby plant seems likely to grow rapidly and compete for light or nutrients, a plant may accelerate its own growth.

If the neighbour appears slower and more oriented towards defence, the receiving plant may instead redirect more energy towards protection.

“VOC receiver plants adjusted their growth to match the competitive pressure signaled by their neighbor’s scent: they grew more when exposed to a fast-growing neighbor and less when exposed to a slow-growing one,” said Dr. Ninkovic.

“This effect was seen consistently across all parts of the plant leaves, stems, and roots rather than the plant simply reshuffling resources between its parts.”

Genes showed the same pattern

The team also measured gene activity.

This was important because it showed the observed growth differences were not merely superficial - the plants were shifting internally.

When Fairytale was exposed to signals from fast-growing Salome, many genes associated with stress and defence became less active, suggesting the plant was moving energy towards growth.

When Salome received signals from slow-growing Fairytale, more than 2,000 genes increased in activity. Many of these were tied to DNA replication, protein activity, and defence-related processes.

So the response was not only about how the plants looked or grew; their underlying biology was also being reshaped by chemical information from neighbours.

Each plant smells different

The researchers then analysed the chemical blends emitted by each barley cultivar.

Across the three cultivars, they detected 115 volatile compounds. Each variety produced a distinct chemical profile - effectively, a scent signature.

Using these profiles, a computer model was able to determine which cultivar produced a given chemical sample with 93.1 per cent accuracy, indicating that the differences were substantial.

Fairytale emitted more benzyl nitrile, a compound associated with insect-repellent effects. Salome produced higher amounts of 1 octen 3 ol. Nonanal occurred more often in Fairytale and Luhkas than in Salome.

These chemical contrasts could enable nearby plants to sense whether a neighbour is more geared towards growth or towards defence.

Competition starts early

We typically imagine plant competition in physical terms: roots vying for water, leaves competing for sunlight, and taller plants shading those beneath.

This study implies that competitive interactions may begin before any direct contact or resource conflict occurs.

A plant may detect a fast-growing neighbour through airborne chemicals and start adjusting its growth strategy ahead of time, using scent as an early indicator of future pressure.

That perspective makes plant life seem far more responsive than we have often assumed.

Plants do not have brains, and they do not think as animals do. Even so, they can detect information, react to it, and change how they distribute their limited resources.

How farming could change

These results may have practical implications for agriculture.

Many farms plant a single crop variety across large areas. At the same time, there is growing interest in mixing cultivars to boost resilience and reduce reliance on pesticides.

Until now, decisions about cultivar selection have generally centred on visible traits such as growth rate, disease resistance, and root depth.

This work suggests an additional consideration: chemical compatibility.

If crop varieties influence one another via airborne signals, then certain combinations could enhance growth, defence, or pest resistance, while poorly matched mixtures might suppress performance.

More research is needed before farmers can apply this widely, but the findings point to a promising direction for crop science.

Chemicals that carry messages

VOCs may be a key route through which this sort of information travels.

Rather than being mere by-products, these compounds can act as meaningful signals that influence growth, defence, and gene activity.

“Plants release a rich blend of volatile compounds as a normal part of their biology, and it would make evolutionary sense for neighbors to have developed the ability to pick up on each other’s chemical signals over millions of years of co-existence,” said Dr. Ninkovic.

“We believe this type of constitutive VOC interaction may likely be widespread across the plant kingdom, though the specific compounds involved and the strength of the response will probably vary greatly between species.”