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

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.