Seeds accelerate germination at beneficial planting depths by sensing the sound of rain.

The ability of natural environmental sound to stimulate seeds and seedlings sufficiently to foster growth has not been previously demonstrated or quantified. To study this, rain sound is a logical starting point. Rain produces extremely high amplitude sound pressure with commensurate particle displacements in the upper soil, puddles and wetlands where many plant seeds germinate. Experiments were conducted with controlled rain drops impacting soil and shallow water puddles containing submerged seeds of rice (oryza sativa). Germination rates were measured as the peak sound pressure of drop impact was varied. The displacements of micro-meter-scale statoliths relative to the structure of specialized seed cells that sense gravitational direction were estimated as a function of the controlled rain sound forcing. The results here indicate rice and related seed types can sense the sound of rain impacting the soil or water surface above them and respond by accelerating germination at depths where impulsive rain sound is sufficiently intense to intermittently shake statoliths from contact with cell membrane receptors and trigger gravitropic growth mechanisms. The ability to perceive rain sound and respond with accelerated germination is found to be roughly limited to the relatively shallow depths that are also beneficial to seedling survival.