# Biochemical and anatomical leaf characteristics of oak trees contribute to differences in photosynthetic capacity between leaf habits

## TL;DR

Deciduous oak leaves have higher photosynthetic capacity than evergreen oak leaves due to differences in biochemistry and leaf anatomy.

## Contribution

The study reveals how leaf structure and biochemistry in deciduous oaks enhance photosynthesis to compensate for their shorter growing season.

## Key findings

- Deciduous oak leaves have higher photosynthetic capacity, carboxylation rate, and electron transport rate than evergreen oak leaves.
- Deciduous leaves have denser mesophyll, more palisade mesophyll, and greater mesophyll surface area.
- These anatomical features support higher photosynthetic capacity in deciduous species.

## Abstract

Since the leaf is the primary site of photosynthesis, leaf habit impacts the period over which a plant can acquire carbon. However, leaf biochemistry and anatomical characteristics that contribute to differences in photosynthetic capacity between leaf habits deserve further attention. Using a comparative framework, we examined photosynthetic capacity between oak species (Quercus spp.) with different leaf habits. We performed gas exchange measurements and micro-computed tomography imaging of leaves to compare their biochemical and anatomical characteristics between evergreen and deciduous oak species and to link these leaf characteristics as drivers of photosynthetic capacity. Deciduous species had higher photosynthetic capacity than evergreen. Deciduous leaves had higher maximum carboxylation rate of Rubisco, maximum rate of electron transport, and rate of triose phosphate utilization than evergreen leaves. Their higher photosynthetic capacity was also influenced by leaf anatomical characteristics. Deciduous leaves had more densely packed mesophyll, a greater portion of palisade than spongy mesophyll, and a higher mesophyll surface area than evergreen leaves. Overall, our work suggests that greater investment in leaf structures such as densely packed palisade mesophyll facilitates higher photosynthetic capacity in deciduous species and helps compensate for their shorter growing season.

We used a comparative framework to demonstrate how the biochemistry and internal anatomy of deciduous oak leaves support greater photosynthetic capacity than evergreen oak leaves. Deciduous oaks invest more in leaf structures for light absorption that facilitate higher photosynthetic capacity to compensate for their shorter growing season than evergreen oaks.