Leaf cell wall properties and stomatal density influence oxygen isotope enrichment of leaf water

Measurements of oxygen isotope enrichment of leaf water above source water (Δ¹⁸ O_LW ) can improve our understanding of the interaction between leaf anatomy and physiology on leaf water transport. Models have been developed to predict Δ¹⁸ O_LW such as the string-of-lakes model, which describes the mixing of leaf water pools, and the Péclet effect model, which incorporates transpiration rate and the mixing length between unenriched xylem and enriched mesophyll water in the mesophyll (L_m ) or veins (L_v ). Here we compare measurements and models of Δ¹⁸ O_LW on two cell wall composition mutants grown under two light intensities and relative humidities to evaluate cell wall properties on leaf water transport. In maize (Zea mays), the compromised ultrastructure of the suberin lamellae in the bundle sheath of the ALIPHATIC SUBERIN FERULOYL TRANSFERASE mutant (Zmasft) reduced barriers to apoplastic water movement, resulting in higher E and, potentially, L_v and, consequently, lower Δ¹⁸ O_LW . The difference in Δ¹⁸ O_LW in cellulose synthase-like F6 (CslF6) mutants and wild-type of rice (Oryza sativa) grown under two light intensities co-varied with stomatal density. These results show that cell wall composition and stomatal density influence Δ¹⁸ O_LW and that stable isotopes can facilitate the development of a physiologically and anatomically explicit water transport model.