Water is important for life. It is a primary source of structure and function in all life forms, even including viruses that use it as interstitial fluid for containing their viral genome. For organisms that produce their own complex compounds, commonly known as autotrophs, water remains the main source of outside material they need to keep on living.

Where To Grow

As the quintessential example of autotrophs, plants are no exception. Their root systems grow deep and wide to obtain pockets of water in the soil and to keep their cells nourished. It has long been known that how these roots grow is down moisture gradients, toward wetter patches of soil. This allows them to find water in their soil environment.

But how do they discover it initially? How do they know what direction to grow in? For practically all plants, it’s not like they can physically move themselves to better growing conditions. They have to use what is available to them. Therefore, for soil that doesn’t have any easily noticeable moisture gradients, how do plants determine which direction to grow their roots in order to find water?

Growing in every direction isn’t usually an option. It would require too much energy and effort to extend their root systems in so many paths. While some plants do use web-like roots, there is still a directional flow to their growth. How this flow was decided upon for plants has long been a question for botanists that look into plant growth and nutrient uptake from the soil.

Sound Is The Key

Now, researchers from the University of Western Australia may have an answer to that question and it reveals a whole new structural side to plants and what senses they have available to them. Using the pea flower plant, Pisum sativum, what could be said to be the original model organism a la Gregor Mendel, they were able to set up a experimental system to test plant roots.

It was placed into a soil container with two potential openings for roots to grow through. Next they used played sounds of running water and water moving through pipes, directing this sound through one pipe or the other.

What they found was that, without any moisture gradient to tell by, the plant will grow its roots toward the vibrational sounds of water. The only available sense was sound vibrations. They also made sure to do a control test that showed that plants will still preferentially follow moisture gradients even over water vibrations, but it is still an apparently available secondary sense plants can use if water isn’t detectable with any other method.

Reducing Pollution And Confirming Hypotheses

Another result the test showed was that the existence of other sounds, also known as acoustic pollution, can mask the sounds of water flowing and the plants will no longer be able to determine the direction to grow their roots. This insight opens up new avenues of study to determine if noise pollution from urban environments and other sources may be harming the ability of plants to grow and find water to survive.

Plant bioacoustics has already been a field of study for several years, though more focused on the abilities of some plants to use vibrational sound, or sonication, in order to spread their pollen or attract insects. They also have the ability to use rudimentary communication with their vibrations, similar to chemical signals plants also use, to transfer information to other plants, such as whether they are under attack from some sort of predator.

How they accomplish this (or detect vibrations themselves, including in the soil) is not well understood. Some hypotheses include using individual cells in the roots and other parts of the plants as a physical sounding board for reverberation or by using energy from ATP to create mechanical oscillations in the cytoskeleton to make vibrations, but none of these theories have been able to provide much evidence for confirmation as of yet.

On To More Testing

But adding this new discovery to the list of abilities that plants contain can potentially be the key piece to nail down a definitive and provable hypothesis once and for all. Which, in turn, will allow everyone in the world that works with plants to be able to grow them more efficiently and protect the environment more carefully. And to improve the world we all live in.

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Study Link

Photo CCs: Roots by cesarpb from Wikimedia Commons

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