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

Abstract

Chlorophyll a+ b content (Chl a+ b), stomatal conductance ( g s) and net photosynthesis ( P N) in Arbutus unedo increased with leaf age up to full leaf expansion (0.44±0.001 mg g −1, 0.2±0.01 mol H 2O m −2 s −1, 10.5±0.2 μmol CO 2 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: P N was directly correlated with g s, 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 cm 2 g −1 specific leaf area (SLA), 0.4±0.01 μm leaf tissue density (LTD), and a diurnal trend of leaf inclination ( α) 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.