Leaf age‐dependent changes in structure, nitrogen content, internal mesophyll diffusion conductance (g_m), the capacity for photosynthetic electron transport (J_max) and the maximum carboxylase activity of Rubisco (V_cmax) were investigated in mature non‐senescent leaves of Laurus nobilis L., Olea europea L. and Quercus ilex L. to test the hypothesis that the relative significance of biochemical and diffusion limitations of photosynthesis changes with leaf age. The leaf life‐span was up to 3 years in L. nobilis and O. europea and 6 years in Q. ilex. Increases in leaf age resulted in enhanced leaf dry mass per unit area (M_A), larger leaf dry to fresh mass ratio, and lower nitrogen contents per dry mass (N_M) in all species, and lower nitrogen contents per area (N_A) in L. nobilis and Q. ilex. Older leaves had lower g_m, J_max and V_cmax. Due to the age‐dependent increase in M_A, mass‐based g_m, J_max and V_cmax declined more strongly (7‐ to 10‐fold) with age than area‐based (5‐ to 7‐fold) characteristics. Diffusion conductance was positively associated with foliage photosynthetic potentials. However, this correlation was curvilinear, leading to lower ratio of chloroplastic to internal CO₂ concentration (C_c/C_i) and larger drawdown of CO₂ from leaf internal air space to chloroplasts (Δ_C) in older leaves with lower g_m. Overall the age‐dependent decreases in photosynthetic potentials were associated with decreases in N_M and in the fraction of N in photosynthetic proteins, whereas decreases in g_m were associated with increases in M_A and the fraction of cell walls. These age‐dependent modifications altered the functional scaling of foliage photosynthetic potentials with M_A, N_M, and N_A. The species primarily differed in the rate of age‐dependent modifications in foliage structural and functional characteristics, but also in the degree of age‐dependent changes in various variables. Stomatal openness was weakly associated with leaf age, but due to species differences in stomatal openness, the distribution of total diffusion limitation between stomata and mesophyll varied among species. These data collectively demonstrate that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations. Age‐dependent changes in g_m and photosynthetic capacities do not occur in a co‐ordinated manner in these species such that mesophyll diffusion constraints curb photosynthesis more in older than in younger leaves.

Mature non‐senescent leaves of evergreen species become gradually shaded as new foliage develops and canopy expands, but the interactive effects of integrated light during leaf formation (Q_int^G), current light (Q_int^C) and leaf age on foliage photosynthetic competence are poorly understood. In Quercus ilex L., we measured the responses of leaf structural and physiological variables to Q_int^C and Q_int^G for four leaf age classes. Leaf aging resulted in increases in leaf dry mass per unit area (M_A), and leaf dry to fresh mass ratio (D_F) and decreases in N content per dry mass (N_M). N content per area (N_A) was independent of age, indicating that decreases in N_M reflected dilution of leaf N because of accumulation of dry mass (N_A = N_M M_A). M_A, D_F and N_A scaled positively with irradiance, whereas these age‐specific correlations were stronger with leaf growth light than with current leaf light. Area‐based maximum ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) carboxylase activity (V_cmax^A), capacity for photosynthetic electron transport (J_max^A) and the rate of non‐photorespiratory respiration in light (R_d^A) were also positively associated with irradiance. Differently from leaf structural characteristics, for all data pooled, these relationships were stronger with current light with little differences among leaves of different age. Acclimation to current leaf light environment was achieved by light‐dependent partitioning of N in rate‐limiting proteins. Mass‐based physiological activities decreased with increasing leaf age, reflecting dilution of leaf N and a larger fraction of non‐photosynthetic N in older leaves. This resulted in age‐dependent modification of leaf photosynthetic potentials versus N relationships. Internal diffusion conductance (g_m) per unit area (g_m^A) increased curvilinearly with increasing irradiance for two youngest leaf age classes and was independent of light for older leaves. In contrast, g_m per dry mass (g_m^M) was negatively associated with light in current‐year leaves. Greater photosynthetic potentials and moderate changes in diffusion conductance resulted in greater internal diffusion limitations of photosynthesis in higher light. Both area‐ and mass‐based g_m decreased with increasing leaf age. The decrease in diffusion conductance was larger than changes in photosynthetic potentials, leading to larger CO₂ drawdown from leaf internal air space to chloroplasts (Δ_C) in older leaves. The increases in diffusion limitations in older leaves and at higher light scaled with age‐ and light‐dependent increases in M_A and D_F. Overall, our study demonstrates a large potential of foliage photosynthetic acclimation to changes in leaf light environment, but also highlights enhanced structural diffusion limitations in older leaves that result from leaf structural acclimation to previous rather than to current light environment and accumulation of structural compounds with leaf age.