ASHS 2024 Conference

The leaf surface and interior structure can affect photosynthesis and transpiration rates associated with water use efficiency. Several studies have assessed pecan (𝘊𝘢𝘳𝘺𝘢 𝘪𝘭𝘭𝘪𝘯𝘰𝘪𝘯𝘦𝘯𝘴𝘪𝘴) leaf anatomical traits and established differences between cultivars; however, the effect of these traits on water use efficiency across cultivars has not been established. Understanding the relationship between leaf anatomical structures and water use efficiency across pecan cultivars allows for the identification of those that are well suited for water limited environments. In this study, we examined the leaf mesophyll layer thickness (µm), trichome density (trichome mm⁻²), stomatal density (stomata mm⁻²), and stomatal pore area (µm²) of four pecan cultivars (‘Wichita’, ‘Western’, ‘Pawnee’, and ‘Lakota’; all grafted to clonally propagated rootstocks). Leaves were collected at the NMSU Leyendecker Plant Science Research Center, and their cross-section and abaxial surface were imaged using light and scanning electron microscopy, respectively. ‘Lakota’ leaves had the thinnest palisade mesophyll layer and thickest spongy mesophyll layer relative to total leaf thickness. The stomatal density of ‘Pawnee’ was significantly less than the other cultivars, but no significant differences in stomatal pore area were observed. Intrinsic water use efficiency, calculated as ratio of the carbon assimilation rate to stomatal conductance to water vapor, was obtained using a leaf gas exchange meter on three separate days. A stable carbon isotope composition analysis was also conducted to provide insight into the leaf’s longer-term water use efficiency. The results showed that the intrinsic water use efficiency of ‘Lakota’ was different from ‘Western’ on one of the days; however, differences between cultivars were not significant when averaged across the measurement dates. Furthermore, the relative ¹³C abundance and ¹³C discrimination did not have significant differences across the four pecan cultivars evaluated, suggesting that differences in leaf anatomical traits did not influence the water use efficiency of these samples.