Abstract
Tension wood is a reaction wood of angiosperm woody plants. Reaction wood causes the stem to bend by its mechanical action. Tension wood generates much higher tensile growth stress than normal wood. However, the mechanism how the tissue generates tensile stress in tension wood is still unknown. Water potential in the stem of woody plants has circadian rhythm caused by the alteration of the balance between transpiration and absorption. Since this water rhythm has enough force to change the stem diameter, the rhythm could generate tensile stress of tension wood. Then, poplar trees were grown horizontally in growth chamber and the strain of the stem was measured. The result from the longitudinal upper side showed different profile from those of lower side or transverse position. This result shows that water potential could play a role for generating the tensile stress of tension wood.
