The frequency of voices human can hear is confined to 20-20000Hz. However, our lives will be very different if we can hear vibrations over 20000Hz. Sounds made by plants are one of them.
Though counterintuitive, plants can also make 'airbone cry' under water-deprived or stressed circumstances according to Lilach Hadany and her colleague at Tel-Aviv University in Israel. The team finds the sound similar to 'a bit like popcorn — very short clicks', Hadany says, 'It is not singing.'
Specifically for Hadany's team, they devised a machine learning algorithm that could detect cries of plants after filtering out environmental noises. It was then tested in a greenhouse where tomato, tobacco, weat, and whine grapes plants are all presented. With an algorithm accuracy of 70%, there seems to be a consistent trend that plants make noises when they are thristy or pressured regardless of plant types.
Results showed that cut plants with little access to water produce around 35 sounds per hour, compared to their water-rich and uncut counterparts making only about one sound per hour. These cries fall in the frequency range of 20 to100 kilohertz, rendering normal human virtually unable to notice plants' moans.
But what's the molecular basis? Hadnay and her colleague hypothesized that bubbles in plant xylem is primarily responsible for making airbone cracks. Bubble breaking and forming due to surface tension in xylem might make a little popping noise. Plants subjected to drought stress are more likely to form bubbles, and thus explaining their minute cries.