Can seeds hear rain?

​I just learned that seeds grow better when they sense the impact of rain.
 
Does this mean they hear it the same way we do? No, of course not. We’ve already asked the question Can plants hear in an earlier post. But it amazes me that the sound vibrations caused by rain striking the soil change the way seeds grow.
 
Let’s find out more.

Water and soil splashed by the impact of a single raindrop (USDA)

According to recent research conducted at the Massachusetts Institute of Technology, published in the journal Scientific Reports, seeds exposed to the patter of water droplets sprout 30-40% faster than seeds living without that experience.
 
That’s huge! But how does it work?
 
It turns out that many seeds have tiny structures called statoliths. Statoliths are responsible, at least in part, for plant gravitropism. These gravity-sensing organelles are rattled when rain hits nearby soil or puddles. These awoken statoliths then signal the seed to germinate.
 
Nicholas C. Makris and Cadine Navarro conducted the study. Professor Makris described statoliths like “sand in a jar of water”.  When we plant a seed, it gets moved around quite a bit. Similar jostling occurs when seeds fall to the ground, are blown around by a breeze, or pass through a digestive system. When the seed finally stops moving, the statoliths settle to the bottom of the cell, indicating which way is up for stems and down for roots.
 
What really surprised me was that the sound of a drop of rain hitting water is extremely loud to a seed. According to Professor Markis, “if you’re a seed that’s within a few centimeters 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 meters of a jet engine in the air.” I had no idea.
 
Earlier, I said I was amazed, but I guess I shouldn’t be. It makes sense. If seeds wait for rain to fall before germinating, they will be more likely to thrive.
 
Did you know that raindrops are never teardrop-shaped? Small raindrops are spherical, and larger raindrops are flattened on the bottom because of the air pressure.
 
OK, I’m still amazed. And maybe it’s time to turn on the sprinklers…