How plants can talk: emitting informative airborne sounds under stress

Stressed plants show altered phenotypes, including changes in color, smell, and shape. Yet, the possibility that plants emit airborne sounds when stressed – similarly to many animals – has not been investigated. Here CSH, the Cold Spring Harbor Laboratory, shows, to their knowledge for the first time, that stressed plants emit airborne sounds that can be recorded remotely, both in acoustic chambers and in greenhouses.

"We recorded ∼65 dBSPL ultrasonic sounds 10 cm from tomato and tobacco plants, implying that these sounds could be detected by some organisms from up to several meters away", they explain. "We developed machine learning models that were capable of distinguishing between plant sounds and general noises, and identifying the condition of the plants – dry, cut, or intact – based solely on the emitted sounds."

The results suggest that animals, humans, and possibly even other plants, could use sounds emitted by a plant to gain information about the plant’s condition.

The research was conducted in growth rooms and greenhouses. as well.

Tomato and tobacco were used in all the experiments. All the plants were grown in a growth room at 25 °C and kept in long-day conditions (16 h day, 8 h night). The plants were tested in the experiments 5-7 weeks after germination.

Research

To investigate plants’ airborne sound emissions, we first constructed a reliable recording system, where the plants were recorded within an acoustic box, and then tested the system in a greenhouse.

To investigate plants’ ability to emit airborne sound emissions, they first constructed a reliable recording system, in which each plant was recorded simultaneously with two microphones, within an acoustically isolated anechoic box. They recorded the plants under different treatments – drought stress, cutting (of the stem), and controls and focused on the ultrasonic sound range (20-150 kHz), where the background noise is weaker.

Results from the acoustic box recordings showed that drought-stressed plants emitted significantly more sounds than control plants. "We thus used the number of tomato sounds emitted within an hour of recording to distinguish between drought-stressed plants and control plants, in the greenhouse. Each plant was recorded either one day after watering (control) or five days after watering (drought-stressed). This classification method, which only counted plant sounds, achieved ∼84% accuracy, significantly distinguishing between drought-stressed and control tomato plants", the researchers say.

"We continued to study the acoustic manifestation of the dehydration process, by recording tomato plants for ten consecutive days. Each tomato plant was watered, and then placed in the greenhouse for ten days of recording without watering. We used a model to separate tomato sounds from greenhouse noises. We then counted the tomato-classified sounds recorded on each day from each tomato. These results revealed a consistent acoustic pattern: the plants emit very few sounds when irrigated, the number of sounds per day increases in the following 4-6 days, and then decreases as the plant dries."

More investigation on plant bioacoustics in general and on sound emission in plants in particular may open new avenues for understanding plants and their interactions with the environment, and it may also have a significant impact on agriculture.

Read more about the research here.