Changes in morphological and physiological traits during leaf expansion of Arbutus unedo

Chlorophyll a+b content (Chl a+b), stomatal conductance (gs) and net photosynthesis (PN) in Arbutus unedo increased with leaf age up to full leaf expansion (0.44±0.001 mg g−1, 0.2±0.01 mol H2O m−2 s−1, 10.5±0.2 µmol CO2 m−2 s−1 respectively), and the average daily leaf inclination decreased from 64.0±2.0° (13 days after bud break) to 50.4±5.2° at full leaf expansion. The correlation analysis of the data sets collected during leaf development confirmed the dependence among structural and functional traits in A. unedo: PN was directly correlated with gs, leaf dry mass (DM), leaf area (LA), and Chl a+b. At full expansion, leaves were characterised by a well-developed palisade parenchyma (two layers), 1.06 ratio palisade/spongy parenchyma, 395±10 µm leaf lamina thickness (L), 67.8±0.2 cm2 g−1 specific leaf area (SLA), 0.4±0.01 µm leaf tissue density (LTD), and a diurnal trend of leaf inclination (°) with a maximum at midday (up to 63.9±0.3°) determining 48% reduction of incident irradiance. By these specific leaf traits A. unedo might be considered as an evergreen scherophyllous species at low degree of sclerophylly.