Trees can sense their own shape and straighten their trunks with muscle-like wood

Young poplar trees laid on their sides bend back toward vertical, and researchers in France now say how. Bruno Moulia and colleagues at INRAE found that the trees sense the curve of their own stems and respond by growing tension wood on the opposite side, a tissue that pulls the trunk straight. Moulia calls it a genuine sensorimotor loop operating in the woody parts of trees.

Tech news in one quick read: Get the most interesting stories in startups, tech and programming, each with a short TLDR, in one daily email from TLDR.

Subscribe to TLDR →

We may earn a commission if you sign up.

Wood is usually thought of as inert structure. The experiment suggests that, at least where it forms, it behaves like a working muscle.

Proprioception in a poplar

Proprioception is the sense of where the parts of a body are, the faculty that lets a person touch their nose with eyes closed. A team including INRAE researchers showed in 2012 that plants have it too, in a paper in PNAS, overturning the idea that the sense belonged to animals. The new work asks what a tree does with that information once the stem is wood rather than soft tissue.

The study, titled “Proprioception drives tension wood formation for autotropic straightening and postural control in trees,” appeared in New Phytologist. Its eight authors, including first author Caulus, Hartmann, Decourteix and Moulia, work in the PIAF research unit shared by INRAE and Université Clermont Auvergne.

Plant scientists have a name for the tendency to overlook plants, plant blindness, and New Atlas, in its report on the study, ties the finding to that gap. The 2012 result that plants have a body sense had already been surprising. Explaining how the sense gets turned into a physical correction, in the woody part of a tree that cannot move, is the step the French group has now documented.

Tipping poplars and removing the cues

The design had to strip away the usual guides. Gravity and light normally tell a tree which way is up, so the team first laid young poplars horizontally until they curved upward, which took about ten days. They then moved the trees onto a clinostat, a horizontal platform that rotates around its axis inside a sphere lit evenly from all directions. With constant gravity direction and directional light cues removed, the only information left was the tree’s own shape.

The timing mattered. Each tree spent about ten days horizontal, long enough to develop a visible curve in its trunk, which gave the clinostat experiment something to correct. A tree that had never been bent would show nothing, and a tree left in normal conditions would straighten using gravity and light, which would hide any contribution from shape sensing. By removing the external cues, the researchers could attribute the straightening to the tree’s internal sense of its own curvature.

The INRAE press release explains what happened next. Tension wood on the upper side of the stem, which had pulled the tree upward, stopped forming once the device was running. The same tissue began forming on the opposite flank, and over a few weeks it pulled the stem back until it was nearly straight.

Tension wood as an opposing muscle

Tension wood generates a pulling force along the stem as it forms. Before this work, researchers had understood it as forming only on the upper side of a leaning stem, where it lifts the trunk. The new result gives it a second job. Formed on the other side, it acts as an antagonist, the way one muscle in an arm opposes another.

ScienceDaily’s account of the INRAE work quotes Hartmann saying that revealing the capabilities of trees requires a great deal of ingenuity, a nod to the apparatus needed to separate shape sensing from gravity and light. The authors stress that real trees combine proprioception with those other cues rather than relying on it alone.

The result also reframes how a tree is understood to hold its posture. Rather than relying on a single reference such as gravity, the authors say plants combine proprioception with cues from light and gravity to maintain their posture. Shape sensing supplies the correction signal when those external cues are weak or conflicting, such as on a slope, in a dense canopy or after wind has bent a stem. In a stem that has already turned to wood and cannot simply be rebuilt, a tissue that can pull in either direction is a flexible repair tool.

The practical hopes are concrete but unproven. INRAE says the mechanism could help breed cereals that resist lodging, where stems flatten in wind and rain, and could improve timber quality, since poorly coordinated tension wood can leave excess internal stress in lumber. Trees with strong shape sensing might also stand up better to storms and landslides on slopes. New Atlas adds that the process is separate from turgor pressure, the water-driven stiffness that also shapes plant tissue. Poorly coordinated tension wood, the INRAE team notes, can leave excess internal tension in a trunk and lower the quality of the wood that comes from it. The next open question is how widely the same loop operates beyond young poplars, particularly in older, thicker trunks.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

Tech news in one quick read: Subscribe to TLDR →

We may earn a commission if you sign up.