Leaf orientation, light interception and stomatal conductance of Eucalyptus globulus ssp globulus leaves

Juvenile and adult leaves of the heteroblastic species Eucalyptus globulus Labill. ssp. globulus did not show active diurnal orientation toward or awa y from incident radiation. Juvenile leaves of a late-maturing sapling of a Tasmanian provenance were evenly distributed in all azimuth sectors. In con trast, an early-maturing sapling of the same age from Wilsons Promontory, V ictoria had a predominance of adult leaf blades facing east and west. Mid-v ein and blade angles of juvenile and adult leaves were non-random with an o verall vertical declination of the leaves. Both leaf types intercepted a gr eater irradiance during the morning than at midday. Sub-horizontal juvenile leaves intercepted 22% more irradiance than vertical adult leaves during t he middle of the day. The amphistomatal and isobilateral adult leaves inter cepted sunlight equally on both leaf surfaces. Stomatal conductance was var iable during the period of measurement but was similar for the Tasmanian ju venile (0.4 to 0.9 cm s(-1)) leaves and Wilsons Promontory adult (0.5 to 1. 2 cm s(-1)) leaves. Greater light interception by the sub-horizontal juveni le leaves would confer a growth advantage to saplings and regenerating cano pies. Reduced light interception and leaf temperature of vertical adult E g lobulus leaves would assist in water conservation, particularly at high sol ar angles.