Water uptake, diameter change, and nonlinear diffusion in tree stems.

Area of Science:

• Plant physiology
• Biophysics
• Water transport in plants

Background:

• Phloem plays a crucial role in nutrient and water transport within plants.
• Understanding phloem swelling and contraction dynamics is essential for plant water relations.
• Existing models may not fully capture the moisture-dependent nature of water movement in phloem.

Purpose of the Study:

• To propose and validate a novel diffusion model for phloem swelling and contraction.
• To investigate the relationship between water movement rate and phloem moisture content.
• To explain the observed lag in stem shrinkage relative to foliage water potential.

Main Methods:

• Development of a diffusion model incorporating moisture-dependent water movement rates.
• Experimental validation using cotton stem phloem swelling.
• Analysis of stem shrinkage dynamics in relation to foliage water potential.

Main Results:

• The proposed diffusion model showed good agreement with actual cotton stem phloem swelling.
• The model indicates that water moves more readily into wetter phloem tissues.
• The model successfully explains the lag in pine stem shrinkage behind foliage water potential, linking it to phloem thickness.

Conclusions:

• The developed diffusion model provides a robust framework for understanding phloem water dynamics.
• Phloem moisture content significantly influences the rate of water movement, affecting swelling and contraction.
• Phloem thickness is a key factor contributing to the temporal lag in stem shrinkage responses to changes in foliage water potential.