Trees straighten themselves using opposing muscle-like wood, study finds
Researchers working with INRAE have found that trees sense their own shape and right a lean by growing tension wood on opposite sides of the stem.
Trees can correct a leaning trunk by growing a special kind of wood on opposite sides of the stem, with each side pulling against the other much as paired muscles do. The finding, from researchers working with the research institute INRAE, answers a question that has lingered for years: how does a plant turn a sense of its own shape into movement?
Scientists have known since 2012 that plants have proprioception, an awareness of their own posture that was once believed to belong to animals alone. What nobody had pinned down was the biology that converts that awareness into physical action.
To find out, the team had to strip away the usual clues. Young poplars were first laid on their sides, and their stems gradually curved upwards. After about ten days, once the bend was obvious, the trees were moved onto a rotating horizontal platform inside a sphere lit evenly from every direction. With gravity giving no steady signal and light offering no hint of which way was up, the trees were left to rely on their own sense of shape.
Over the following weeks, the bent stems slowly became almost straight. When the researchers examined the wood, they found that the tension wood on the upper side, which had been hauling the stem upwards, had stopped forming. Identical tension wood had started to appear on the opposite side, pulling the other way and easing the stem back into line.
Until now, tension wood was thought to form only on the upper side of a leaning stem. The new work shows it is a good deal more versatile, and that a tree’s internal sense of its form helps decide where it develops.
Bruno Moulia, INRAE research director, said the team had found a feedback loop between sensing and movement in the woody parts of trees. He added that poor coordination of tension wood can leave a tree with too much internal strain, which can affect the quality of its timber.
The practical possibilities are promising. Scientists may be able to pick out varieties with particularly good proprioception, which could grow straighter and give better wood. The same knowledge might help breeders develop cereal crops that are less likely to topple before harvest, a problem known as lodging.
Why it matters
Storms, landslides and other extreme events can bend or push over trees, and climate change is expected to expose forests to more of them. Understanding how trees right themselves could help foresters and plant breeders choose resilient varieties. It could also lead to better timber, since badly coordinated tension wood can build up stress inside a trunk. For crops, sturdier stems could mean fewer losses at harvest time, which would be a welcome boost for farmers.
