Vascular optimality dictates plant morphology away from Leonardo's rule

Area of Science:

• Plant physiology
• Biophysics
• Ecology

Background:

• Metabolic scaling theory (MST) explains organismal morphology.
• Vascular plants exhibit universal tip-to-base conduit widening.
• Previous models assume constant sapwood area, contradicting empirical data.

Purpose of the Study:

• Develop generalized MST (gMST) relationships for plant vascular systems.
• Incorporate variable conduit coalescence and taper.
• Reconcile and extend MST to the entire plant structure.

Main Methods:

• Developed a gMST model with distal coalescence.
• Derived relationships between stem taper and conduit widening.
• Compared gMST predictions with empirical data and previous models.

Main Results:

• Plant morphology is dictated by vascular optimality, not constant sapwood area (contradicting Leonardo's rule).
• Energy efficiency controls conduit coalescence, lowering carbon costs.
• Taller plants require increased conduit widening and coalescence, potentially increasing drought vulnerability.

Conclusions:

• gMST provides a more accurate prediction of vessel dimensions and frequency than previous MST models.
• Energy efficiency is a key factor in plant carbon allocation and vascular network maintenance.
• Further research is needed to empirically validate gMST predictions, such as conduit coalescence rates.