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

Authors: MOMAYYEZI, MINA - University Of California, Davis; PRATS, KYRA - Purdue University; McElrone, Andrew; FURZE, MORGAN - Purdue University

Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2025
Publication Date: 11/3/2025
Citation: Momayyezi, M., Prats, K.A., Mcelrone, A.J., Furze, M.E. 2025. Biochemical and anatomical leaf characteristics of oak trees contribute to differences in photosynthetic capacity between leaf habits. AoB Plants. Volume 17, Issue 6, December 2025. https://doi.org/10.1093/aobpla/plaf063.
DOI: https://doi.org/10.1093/aobpla/plaf063

Interpretive Summary: Heat waves (HWs) pose a significant threat to California agriculture, with potential adverse effects on crop photosynthetic capacity, quality and yield leading to significant economic loss. Lack of heat resilient cultivars puts perennial crop production under severe threat with increasing HW frequency, duration and intensity. Currently available walnut cultivars are highly sensitive to abiotic stress, and germplasm collections provide potential solutions via genotypes native to varied climates. We screened 9 English walnut accessions (Juglans regia) for physiological heat stress resilience and recovery in the USDA-ARS National Clonal Germplasm over two-years, and identified accessions with superior resilience to heat stress. Photosynthetic capacity, assessed as net and maximum assimilation rates (An and Amax, respectively), quantum efficiency of PSII and stomatal conductance (gs), was consistently reduced by heat stress for all accessions, but remained higher and/or recovered completely for a few accessions after HW events. Irrigation delivered during HWs, which is commonly used to mitigate detrimental effects of heat stress, improved photosynthetic recovery for several accessions, especially for A3 & A5. These same accessions exhibited the highest An under non-stressed conditions and at ambient temperatures of 35° to 45°C. Higher performance for A3 and A5 under HWs was associated with greater carboxylation rates, electron transport rates, and carbonic anhydrase activity and changes in leaf reflectance spectral indices. All accessions suffered significant declines at 45°C; ambient leaf temperatures approached this level for some accessions during record setting heat waves in September 2022, suggesting severe threat to the economically important walnut growing regions in California under future climatic conditions.

Technical 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.