Regression coefficient (R 2), P -values and type of regression model fit are shown. R 2is shown in bold when P ≤ 0.001 (***), P ≤ 0.01 (**),P ≤ 0.05 (*) and P ≤ 0.1 (+). Smes, total mesophyll cell surface area exposed to intercellular air space per unit of leaf surface area; Sc, chloroplast coverage of Smes, gm, mesophyll conductance to CO2 diffusion estimated by Ogee et al . (2018); mesophyll cell wall thickness (MCW); SDada, adaxial stomatal density; SDaba, abaxial stomatal density; SR, stomatal ratio; Narea, leaf N content expressed on area basis; stomatal conductance to water vapor diffusion (gsw); VED, average vein-to-epidermis distance; VEDada, vein-to-adaxial epidermis distance; VEDaba, vein-to-adaxial epidermis distance; IVD, interveinal distance; total VLA, vein length per unit leaf area; BSCW, BS cell wall thickness; BSias, BS exposed to intercellular air spaces; BS area ratio (calculated as (BS area/ [BS area + Mesophyll area]).