Science & Technology

Trees May Have a "Heartbeat"

It seems like every day we're learning something new about how plants and people aren't so different. We've already told you about how plants can hear when they are being eaten, and how grass screams every time you cut it. Now, it turns out trees seem to have a heartbeat — and they don't even have hearts.

Tree Still, My Beating Heart

There is a certain rhythm to life. Humans tend to wake up in the morning and go back to sleep at night based on a cycle we call a circadian rhythm. Other patterns, like your digestive cycle and the rhythm of your breathing, are faster than the rising and the setting of the sun. And then there's your heartbeat, pounding faithfully away more than 2 billion times through your life. Scientists have known about some of the slower rhythms in a tree's life cycle, but a new study has shown that at least some trees seem to have a "heartbeat" that has a similar purpose to yours: it pumps fluids throughout the tree's "body."

Speaking with New Scientist, study lead András Zlinszky discussed how this new conception of plant physiology differed from older models. According to the conventional interpretation, the higher parts of the tree are reliant entirely on water collecting and eventually evaporating on the lower leaves. But when Zlinszky and his colleague Anders Barfod examined 22 different species of trees in windless, sunless conditions, they found the branches would move on their own over the course of several hours. That's slow enough to miss, but it's a lot faster than any previous biological process we'd spotted in our tree friends. That slow pattern made the researchers think the evaporation theory couldn't hold water, and a pulse-like pattern might be a better explanation. Or, in the man's own words, "We've discovered that most trees have regular periodic changes in shape, synchronised across the whole plant and shorter than a day-night cycle, which imply periodic changes in water pressure."

The exciting part is that we might have a new explanation for a part of plant physiology that never quite sat right with botanists. But the bad news is that we still don't know exactly how it works. Citing the fact that researchers have recorded tree trunks shrinking up to 0.5 millimeters over the course of a day, the researchers suggest that this might be part of the mechanism that would squeeze water up the trunk of the tree. In any case, there's a lot more to learn about how the whole thing works.

Trees Catching Z's

This wasn't the first time Zlinszky dove deep into the surprising activity going on deep in the forest. In 2016, he measured trees' circadian rhythms and discovered that the branches of birch trees would dip as much as 10 centimeters (4 inches) every single night. That drooping might be a matter of photosynthesis dropping off when the sun's not out, but Zlinszky suggests it might also be a result of trees relaxing at night. If trees are stiffening their branches to catch the most rays as possible during the day, then they might let go of that tension at night in order to rejuvenate. Then, in the morning, it's time to stretch out again. Kinda gives a whole new meaning to "tree pose."

There's so much more to learn about what's happening in the inscrutable minds of trees. Check out "The Hidden Life of Trees" by Peter Wohlleben (free with a trial membership to Audible). We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

Plants Can Hear You

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Key Facts In This Video

  1. There is evidence that certain plants respond to the buzzing of bees by releasing pollen. 00:22

  2. Sound causes greater growth in plants than silence does. 01:39

  3. If you stake a tree too tightly, it won't grow as strong because it does need to fight wind. 01:57

Written by Reuben Westmaas May 23, 2018

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