In the Lab, Young Poplars Use 'Muscles' to Correct Posture

Inside a sphere lit from every direction, young poplars lay on a horizontal rotating platform. Over time, they pushed back against that position and moved toward vertical. Researchers from France’s National Research Institute for Agriculture, Food and Environment, or INRAE, and the University Clermont Auvergne say they have identified the mechanism: tension wood, a special kind of wood inside the stem, acts like a muscle to redirect growth.

The result follows a discovery made nearly 15 years ago, when scientists found that plants had a biological mechanism controlling morphology — their form — that had been thought unique to animals. The new experiment went after the missing piece: not whether plants could shape themselves, but how they sensed their position and corrected it.

The setup was deliberately stripped of familiar cues. The young trees first curved upward toward the light after being placed horizontally. Researchers then rotated them in a sphere illuminated from every direction, removing gravity’s role as a driver of vertical growth. They found that tension wood formed on one side of the stem, using a push-pull motion to drive growth upward; it later switched sides, with the two sides working as opposing muscles to straighten the poplar.

INRAE research director Bruno Moulia describes the process as a “genuine sensorimotor loop” operating in the woody parts of trees. Because producing tension wood is energy-intensive, the behavior is more than a passive consequence of growth: it is a strategic response that helps the tree maintain its form. Félix Hartmann, an INRAE research engineer, said the finding depended on bringing together researchers from different disciplines. Moulia says that poor coordination in the successive activation of tension wood results in excessive internal tension, which can affect wood quality.

The concrete payoff is narrow but useful: the mechanism could guide applied research aimed at improving wood quality and obtaining trees that are straighter and more relaxed. The boundary is clear as well. The evidence comes from young poplars in a controlled experiment, so it describes a biological mechanism rather than a demonstrated forestry method. The research was published in New Phytologist.