Parameterizing a model of Douglas fir water flow using a tracheid-level model

Area of Science:

• Plant Physiology
• Biophysics
• Forest Science

Background:

• Existing theories on tree water flow lack comprehensive mechanistic understanding.
• Numerical modeling offers a powerful approach to investigate complex biological processes like water transport in trees.

Purpose of the Study:

• To numerically assess a new theory of tree water flow by solving a nonlinear partial differential equation model.
• To determine unknown functions within the model using a tracheid-level simulation of water flow in Douglas fir.
• To compare the model's predictions with experimental data and challenge alternative theories.

Main Methods:

• Developed and numerically solved a nonlinear partial differential equation model for tree water flow.
• Utilized a tracheid-level model simulating flow, cavitation, and pit dynamics in Douglas fir.
• Determined key hydraulic functions (conductivity, saturation change, interfacial area change) from tracheid-level simulations.

Main Results:

• Capacitance in tree water transport is not constant but varies with saturation.
• Cell-wall conductivity significantly influences the observed lag in water flow within conifers.
• The transpiration stream demonstrates robustness, with vertical hydraulic conductivity recovery over 180 days after refilling cessation.

Conclusions:

• Both the tracheid-level and differential equation models support the proposed theory of tree water flow.
• The findings challenge the analogy of tree water flow to electrical current flow.
• Cell-wall conductivity is a critical factor in understanding water movement dynamics in trees.