The sound of rain stimulates growth in rice seeds, a new study from the Massachusetts Institute of Technology finds
By Khadeejah Masud
The ambient sounds of rain during a downpour may be a comforting refuge for us humans, but for plants, it is their anthem for growth. A study conducted on rice seeds by the Massachusetts Institute of Technology (MIT) showed that rice seeds were effectively shaken out of a dormant state, stimulating them to germinate faster than seeds that were not exposed to the same sound vibrations.
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‘What this study is saying is that seeds can sense sound in ways that can help them survive,’ said Professor of Mechanical Engineering at MIT, Nicholas Makris. He revealed this is the first evidence of its kind to suggest an ability in both plant seeds and seedlings to sense sounds in nature, concluding that ‘the energy of the rain sound is enough to accelerate a seed’s growth.’
What is happening to these seeds?
Scientists observed that the seeds interacted with the vibrations produced by a raindrop’s sound waves, typically heard between 13 and 25 kHz. What may sound like a mellow patter to us is strong enough to affect shallowly submerged seeds. They jostle a seed cell’s gravity-sensing organelle known as a statolith, which spurs sprouting in seeds or growth in seedlings.
‘If you’re a seed that’s within a few centimetres of a raindrop’s impact, the kind of sound pressures that you would experience in water or in the ground are equivalent to what you’d be subject to within a few metres of a jet engine in the air,’ said Makris.
Other researchers have also looked into how sounds are formed when rain hits a surface. Scientists at NASA, who studied different sizes of raindrops to analyse global rainfall patterns, suggest that raindrops produce dramatically different sounds as they hit water. Some sizes generate bubbles, and others do not. MIT’s study proved that there is a connection between the sound of a water droplet and a seed’s ability to grow. As rice grows optimally underwater, the researchers propose that there may be a biological advantage for seeds that can sense rain.
But crucially, seeds must strike a fine balance – close enough to the surface to respond to rain vibrations, but deep enough to be able to grow.
How do plants hear the world?
Though plants process sound waves differently from humans, their recognition of noise is remarkable. The idea that plants can respond to vibrations dates back to Charles Darwin, who studied plant movement and sensitivity, and evidence from a recent MIT study suggests that sound-induced movement really does affect their growth.
Horticulturalists and gardeners have often said you should speak life into your plants, with even the UK’s King Charles saying in a 1986 interview, ‘I just come and talk to the plants, really — it’s very important to talk to them. They respond.’
The MIT study suggests it may not be the words themselves, but the vibrations they create – combined with the carbon dioxide humans exhale – that stimulate growth in plants. Like different sizes of raindrops, different voices have been proven to affect how tall a plant grows. The Royal Horticultural Society found that low-level vibrations of around 70 decibels produce this effect, and that women’s voices in particular are more effective than men’s. A tomato plant, spoken to by a female, grew approximately two inches taller than one spoken to by a male in the study.
In this research, researchers stated they were unsure why the female voice caused this effect, positing that it could be related to women’s greater range of pitch or tone that affects the sound waves that hit the plant.
In the same way humans experience sound through vibration, plants possess a remarkable ability to perceive noise and alter their behaviour because of it.
