Solid mechanics of the torus–margo in conifer intertracheid bordered pits

Summary Bordered pits of many conifers include a torus–margo structure acting as a valve that prevents air from spreading between tracheids, although the extent of torus deflection as a function of applied pressure is not well known. Models were developed from images of pits in roots and stems of Picea mariana (Mill.) BSP. A computational solid mechanics approach was utilised to determine the extent of torus deflection from pressure applied to the torus and margo. Torus deflection increased in nonlinear fashion with applied pressure. The average pressure required for sealing the pit was 0.894 MPa for stems and 0.644 MPa for roots, although considerable variation was apparent between individual pits. The pits of roots were wider and deeper than those of stems. For stems, the pit depth did not increase with pit width; thus the torus displacement needed to seal the pit was less than for pits from roots. The pressure required to seal the pit depends upon anatomical characteristics such as pit width and pit depth. Although the torus displacement for sealing was greater for roots because of their greater depth, the pressures leading to sealing were not significantly different between roots and stems.