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

Area of Science:

• Plant anatomy and physiology
• Wood science
• Biomechanics

Background:

• Conifers possess bordered pits with torus-margo structures that function as valves.
• These structures prevent the spread of air bubbles (embolisms) between tracheids, crucial for water transport.
• The precise relationship between applied pressure and torus-margo deflection remains incompletely understood.

Purpose of the Study:

• To computationally model torus deflection in Picea mariana (Mill.) BSP. bordered pits under varying pressures.
• To investigate the influence of pit anatomical characteristics (width, depth) on torus deflection and sealing pressure.
• To compare the sealing mechanics of bordered pits in roots versus stems.

Main Methods:

• Developed computational solid mechanics models based on images of bordered pits from Picea mariana roots and stems.
• Simulated pressure application to the torus and margo to determine deflection extent.
• Analyzed the nonlinear relationship between applied pressure and torus deflection.

Main Results:

• Torus deflection increased nonlinearly with applied pressure.
• Average sealing pressures were 0.894 MPa for stems and 0.644 MPa for roots, with significant individual pit variation.
• Root pits were wider and deeper than stem pits; stem pit depth did not correlate with width, affecting torus displacement for sealing.

Conclusions:

• The pressure required to seal bordered pits is dependent on anatomical features like pit width and depth.
• While root pits require greater torus displacement due to depth, sealing pressures were not significantly different between roots and stems.
• This study provides quantitative insights into the valve function of torus-margo structures in conifer water transport under stress.