NUNZIUM

Have you ever stopped to admire a plant's or a tree's beauty, wondering what secrets they hold in their silent existence? Well, recent scientific research has unveiled an astonishing fact: plants, under stress, emit ultrasonic sounds that can be detected and interpreted by other organisms. This groundbreaking discovery changed our perception of the plant kingdom, which was long thought to be almost silent. Like all living organisms, plants are exposed to various stressors throughout their lives. These stressors can be anything from drought and lack of water to being damaged by insects or other animals. As a result, plants have developed ways to react and adapt to these conditions to ensure their survival. Previously, it was assumed that plants responded to stress primarily through chemical and physical changes. Still, the latest research has added another dimension to our understanding of plant communication: sound.

A series of studies have shed light on the fascinating world of plant bioacoustics. It turns out that when plants are exposed to stress, such as drought or physical injury, they emit sounds within the ultrasonic range of 20-100 kHz. These sounds can be detected from 3-5 meters and are audible to many mammals and insects, such as mice and moths. It is even more fascinating that these ultrasonic emissions can be classified and distinguished based on the type of stress the plant is experiencing. Machine learning algorithms were used in the research to differentiate between sounds emitted by plants under different stress conditions, such as drought and cutting. The classification accuracy reached up to 84%, demonstrating the informative nature of these airborne sounds. Moreover, the study found that the pattern of sound emission correlates with the plant's transpiration rate. In contrast, the daily number of sounds increases during the first days of dehydration and declines as the plant dries up. But what causes these sounds in the first place? One possible explanation is cavitation, a process in the plant's stem. Cavitation is the formation of bubbles in a liquid, which would be the water within the plant's xylem (vascular tissue). The bubbles form due to decreased pressure, which can happen during dehydration or when the plant is cut. The size and dynamics of the bubbles, as well as the diameter of the plant's xylem, could influence the frequency and intensity of the sounds emitted.

The discovery of these ultrasonic sounds emitted by plants has far-reaching implications for science and agriculture. In agriculture, monitoring crops' water and disease states is paramount. Efficient water use is critical, as climate change exposes more areas to drought. With the ability to distinguish between drought-stressed and control plants based on the sounds they emit, this new research could pave the way for more precise irrigation methods, saving up to 50% of water expenditure and increasing crop yield. It could have significant economic and ecological implications, contributing to food security and environmental conservation. The study also raises the possibility that other organisms, such as insects and nearby plants, might have evolved to interpret these sounds and respond to them accordingly. For example, some moths, which use tomato and tobacco plants as hosts for their larvae, can hear and react to ultrasound within the frequency range observed in the study. It is not far-fetched to think that plants might have developed the ability to "listen" to the sounds emitted by their stressed or injured neighbours, adjusting their behaviour to increase their drought tolerance or defence mechanisms.

While the research on plant bioacoustics has opened new doors to understanding plant communication and stress responses, the study still has limitations, and further research is needed. The results were obtained from a limited number of plant species, and whether these findings can be generalized to other plants remains to be seen. Further exploration of the sounds emitted under different conditions, such as various pathogens or life stages, is warranted. Lastly, a deeper understanding of the sound emission mechanisms and the challenges of recording and analyzing plant sounds in the field amidst a broader range of background noises is essential. The discovery of ultrasonic sounds emitted by plants under stress has broadened our understanding of the plant kingdom and unveiled a whole new world of potential applications in agriculture and ecological conservation. It is a reminder that there is still much to learn about the secrets in the seemingly silent world of plants. As we continue to unlock the mysteries of plant communication and bioacoustics, we might find innovative ways to protect our planet's flora and ensure a greener, more sustainable future for all.