Light-mediated constraints on leaf function correlate with leaf structure among deciduous and evergreen tree species

Area of Science:

• Plant Physiology
• Leaf Ecophysiology
• Photosynthesis Research

Background:

• Leaf structure significantly influences photosynthetic efficiency.
• Intra-leaf shading in thicker leaves may reduce mass-based photosynthesis.
• The precise impact of leaf structure on light-dependent photosynthesis requires further investigation.

Purpose of the Study:

• To investigate how leaf structure, specifically leaf mass per area (LMA), affects photosynthetic responses to different light conditions.
• To determine the extent of light-mediated functional limitations in leaves with varying LMA.
• To explore the relationship between LMA and light saturation under unidirectional and bidirectional illumination.

Main Methods:

• Examined photosynthetic rates of broad- and needle-leaves across a wide range of LMA.
• Measured responses to high unidirectional and bidirectional light irradiances.
• Analyzed the ratio of unidirectional to bidirectional photosynthesis (Au/Ab) and its correlation with LMA.

Main Results:

• Photosynthesis increased under bidirectional light for most leaves, except those with very low LMA.
• A strong negative correlation was found between LMA and the Au/Ab ratio, nearing 0.5 for the densest leaves.
• Higher LMA correlated positively with intercellular CO2 partial pressure ratios, suggesting light limitation under unidirectional light.

Conclusions:

• Many C3 leaves may not reach light saturation under high unidirectional illumination due to structural limitations.
• Increasing LMA leads to a greater proportion of chloroplasts functioning at subsaturating irradiance under unidirectional light.
• Leaf structure, particularly LMA, plays a critical role in determining photosynthetic efficiency under varying light conditions.