C₄ photosynthesis and hydraulics in grasses.

Area of Science:

• Plant Physiology
• Evolutionary Biology
• Biophysics

Background:

• C4 photosynthesis involves anatomical changes impacting plant hydraulics.
• C4 plants typically have larger cells and higher vein density, suggesting increased leaf capacitance and hydraulic conductance (Kleaf).
• The C4 pathway enhances water use efficiency, potentially creating a supply-demand mismatch in water relations.

Purpose of the Study:

• To investigate the hydraulic reorganization in C4 and C3 grasses using phylogenetic analyses, physiological measurements, and models.
• To examine how the evolution of C4 photosynthesis affects the relationship between plant hydraulics and photosynthetic capacity.
• To understand the long-term evolutionary adjustments in C4 plant water relations.

Main Methods:

• Phylogenetic analyses of closely related C4 and C3 grass species.
• Physiological measurements of leaf hydraulic conductance (Kleaf), capacitance, turgor loss point, and stomatal conductance.
• Modeling approaches to analyze hydraulic and photosynthetic relationships.

Main Results:

• The evolution of C4 photosynthesis decouples the canonical correlation between maximal assimilation rate (Amax) and Kleaf.
• Younger C4 lineages exhibit higher Kleaf, capacitance, and turgor loss point, with lower stomatal conductance compared to C3 relatives.
• Older C4 lineages show reduced Kleaf and capacitance, likely due to decreased outside-xylem hydraulic conductance and altered leaf intercellular airspace.

Conclusions:

• C4 plants undergo significant hydraulic reorganization during their evolution.
• Over time, C4 plants optimize hydraulic investments to balance water supply with the demands of the C4 carbon-concentrating mechanism.
• Evolutionary trends reveal a dynamic interplay between anatomical adaptations for C4 photosynthesis and plant water relations.