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

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 H2O m(-2) s(-1), 10.5 +/- 0.2 mumol CO2 m(-2) s(-1) respectively), and the average daily leaf inclination decreased from 64.0 +/- 2.0degrees (13 days after bud break) to 50.4 +/- 5.2degrees 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, was directly correlated with g, 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 mum leaf lamina thickness (L), 67.8 +/- 0.2 cm(2) g(-1) specific leaf area (SLA), 0.4 +/- 0.01 mum leaf tissue density (LTD), and a diurnal trend of leaf inclination (alpha) with a maximum at midday (up to 63.9 +/- 0.3degrees) 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. (C) 2002 Elsevier Science B.V. All rights reserved.