A few months ago I wrote about the communication of plants and trees using hormones, which was often when a member species was under threat. However, this is not the complete picture as more research starts to come through of the influence of sound on plants as well as sound being produced by the plants themselves, and the production and measurement of electrical signals.
This is not a new concept – South African born zoologist Lyall Watson in 1973 wrote about the electromagnetic signals of plants connected to a lie-detector which could measure their ‘emotions’ which was dismissed by the scientific community. There is also the Federation of Damanhur, a communal ecovillage in Northern Italy, which have been conducting experiments on plants since 1975. The researchers there have used a variation of a simple electric circuit, known as a Wheatstone bridge to measure unknown electrical resistance. They found that the greatest signal variation occurred in the plants upon the arrival of the person who tended the specific plant most regularly.
Regarding sound, a recent paper1 shows how young roots grow towards sound at 220 Hz which suggests they exhibit a frequency selective sensitivity. Moreover, they recorded the production of sound by plants, measured using a laser Doppler vibrometer, had definite spike-like structures which could not be explained by tension release in their water transport system. The researchers posit that sound could be particular useful for short range communication as well as being much cheaper biologically for plants to produce than hormonal chemicals. They also noted that the reception of sound underpins the behavioural organisation of all living organisms and the relationship with their environment – thus it should not be necessarily deemed as irregular in the life of plants.
What this suggests is that there is much still to learn regarding plants and trees, and these investigations may require interdisciplinary approaches. It also raises questions about the effect of the frequency of human vocal chords on plants, and if specific frequencies of sound can be used to help plants grow, as well as to encourage growth in particular areas of landscape.
1. Towards understanding plant bioacoustics. Gagliano et al. Trends in Plant Science, Vol. 17, Issue 6. pg 323-325, 22 March 2012