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 (+). S_mes, total mesophyll cell surface area exposed to intercellular air space per unit of leaf surface area; S_c, chloroplast coverage of S_mes, g_m, mesophyll conductance to CO₂ diffusion estimated by Ogee et al . (2018); mesophyll cell wall thickness (M_CW); SD_ada, adaxial stomatal density; SD_aba, abaxial stomatal density; SR, stomatal ratio; N_area, leaf N content expressed on area basis; stomatal conductance to water vapor diffusion (g_sw); VED, average vein-to-epidermis distance; VED_ada, vein-to-adaxial epidermis distance; VED_aba, vein-to-adaxial epidermis distance; IVD, interveinal distance; total VLA, vein length per unit leaf area; BS_CW, BS cell wall thickness; BS_ias, BS exposed to intercellular air spaces; BS area ratio (calculated as (BS area/ [BS area + Mesophyll area]).