An Intrinsic Geometric Constraint on Morphological Stomatal Traits.

Area of Science:

• Plant Biology
• Evolutionary Biology
• Plant Physiology

Background:

• A significant negative non-linear relationship exists between stomatal density (SD) and stomatal size (SS) or length (SL).
• This relationship is crucial for understanding plant gas exchange and evolution.
• The underlying cause of this relationship has remained unclear.

Purpose of the Study:

• To investigate the influence of geometric constraints on the relationship between stomatal density and size.
• To clarify the cause of the non-linear negative relationship between stomatal density and size/length.

Main Methods:

• Compiled global data on stomatal density, size, and length.
• Analyzed the log-log scaling slope of the relationship between SD and SS, and between SD and SL.
• Assessed the influence of geometric constraints versus non-geometric effects.

Main Results:

• The log-log scaling slopes for SD-SS and SD-SL relationships were not significantly different from -1 and -2, respectively.
• A substantial geometric constraint was found to influence stomatal density.
• Non-geometric effects caused deviations from a simple power function, but the geometric constraint remained dominant.

Conclusions:

• The inherent geometric constraint likely causes the inevitable non-linear and negative relationship between stomatal density and size.
• Angiosperm species exhibit a lower geometric constraint compared to pteridophytes and gymnosperms, potentially due to smaller stomatal sizes.
• Relaxation of this geometric constraint may allow angiosperms to achieve higher stomatal densities, enabling adaptation to diverse environments.