A recently published study suggests that some plants are capable of using sound to locate water. That's right, sound. Although claims of plants liking or disliking certain types of music still belong in the realm of pseudoscience, this research does suggest that plants may be capable of detecting vibrations in an interpretable way.
To test this idea, Dr. Monica Gagliano of the University of Western Australia germinated pea seeds in specially designed mazes. Each maze looked like an upside-down Y. At the end of each arm, she devised a series of treatments that would force the pea seedlings to "choose" their desired rooting direction. In some treatments she used standing water coupled with water running through a tube. In others she simply played the sounds of running water against the sound of white noise.
The peas were allowed to grow for five days and afterwards were checked to see which direction their roots were growing. Amazingly, the peas seemed to be able to distinguish the sound of actual running water even when there was no moisture gradient present. Peas given the option of sitting or running water in a tube grew their roots towards the tube a majority of the time. Again, this was in the absence of any sort of water gradient in order to eliminate the chances that the peas were simply honing in on humidity.
Interestingly, plants that were played the sound of running water and white noise through speakers seemed to do what they could to avoid the noise. Although the research did not investigate why the peas had an aversion to the recordings, Dr. Gagliano suspects that it might have something to do with the low frequency magnetic currents emitted by the speakers. Previous research has shown that even weak localized magnetic fields are enough to disrupt the structure of developing root cells.
All of this taken together paints a fascinating picture of plant sensory capabilities. One should take note, however, that the sample sizes used in this experiment were quite small. More, larger experiments will be needed to fully understand these patterns as well as the mechanisms behind them. Still, these findings shed light on cases in which tree roots seem to be so adept at finding sewer pipes, even in the absence of leaks. It also lends to the findings that the roots of trees such as scrub oaks and box elders will often opt for more stable and reliable sources of ground water over the fluctuating uncertainty of nearby stream sources. Finally, there is something to be said that we share as many as 10 of the 50 genes involved in human hearing with plants.
Our understanding of plant sensory capabilities is really starting to blossom (pun intended). Plants aren't the static, sessile organisms so many make them out to be. They are living, breathing organisms fighting for survival. I, for one, am excited for what new discoveries await.