Convergence in leaf size versus twig leaf area scaling: do plants optimize leaf area partitioning?

Area of Science:

• Plant biology
• Ecology
• Allometry

Background:

• Corner's rule posits that thicker twigs support larger leaves.
• The precise scaling relationship and underlying mechanisms remain subjects of research.
• Hydraulic and mechanical factors explain total leaf area, but not mean leaf size scaling.

Purpose of the Study:

• Investigate the within-species scaling relationship between twig size and mean leaf size.
• Assess the variability of this relationship across different plant species.
• Develop a model to explain the observed scaling patterns.

Main Methods:

• Compared twig properties across six co-occurring, functionally similar plant species.
• Modeled the economics of leaf display, balancing light absorption benefits against tissue costs.
• Predicted optimal leaf size and number combinations under varying canopy openings.

Main Results:

• Observed a consistent scaling exponent of 0.6 for twig size versus mean leaf size.
• This coordination was specific to twig size and leaf number, not other twig properties.
• The model predicted positive scaling when twigs optimally filled canopy gaps, with the 0.6 exponent explained by reduced self-shading in larger openings.

Conclusions:

• Corner's rule may be better understood as positive twig size by leaf size scaling.
• The developed model offers a potential explanation for observed scaling.
• Environmental factors, such as canopy openness, may influence scaling relationships.