Modelling the hydrodynamic resistance of bordered pits.

Area of Science:

• Plant anatomy and physiology
• Hydrodynamics
• Wood science

Background:

• Resistance to water flow in plant stems is significantly influenced by bordered pits in tracheids.
• The proportion of resistance attributed to pits increases with tracheid diameter, suggesting a potential evolutionary limit.

Purpose of the Study:

• To investigate the hydrodynamic resistance of bordered pits in Tsuga canadensis.
• To estimate the resistance of a single pit and its contribution to overall tracheid and wood resistivity.
• To explore the evolutionary implications of pit resistance on tracheid diameter.

Main Methods:

• Utilized large-scale physical models to study hydrodynamic resistance of bordered pits.
• Varied pit membrane pore size and removed pit components (torus, border) to assess their impact on resistance.
• Incorporated pit resistance estimates into analytical models of tracheid resistance and wood resistivity.

Main Results:

• Estimated the resistance of a single bordered pit to be 1.70x10^15 Pa s m^-3.
• Found pit resistance inversely proportional to pore size (to the power of 0.715).
• Removal of torus reduced resistance by 28%; removal of torus and border reduced it by 72%.
• Pit resistance accounts for an estimated 29% of total resistance in a typical tracheid.

Conclusions:

• Bordered pit resistance is a significant factor limiting tracheid diameter in conifers.
• Wider tracheids necessitate proportionally greater length to minimize hydrodynamic resistance.
• Evolutionary limitations on tracheid cell length or volume, rather than pit resistance alone, may govern conifer tracheid diameter.