© 2000 Heron Publishing—Victoria, Canada
Leaf orientation, light interception and stomatal conductance of Eucalyptus globulus ssp. globulus leaves
Shelley A. James (1, 2) and David T. Bell (1)
1. Department of Botany, The University of Western Australia, Nedlands, WA 6907, Australia / 2. Department of Botany, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822, USA / Received June 30, 1999
Summary
Juvenile and adult leaves of the heteroblastic species Eucalyptus globulus Labill. ssp. globulus did not show active diurnal orientation toward or away from incident radiation. Juvenile leaves of a late-maturing sapling
of a Tasmanian provenance were evenly distributed in all azimuth sectors. In contrast, an early-maturing sapling of the same
age from Wilsons Promontory, Victoria had a predominance of adult leaf blades facing east and west. Mid-vein and blade angles
of juvenile and adult leaves were non-random with an overall vertical declination of the leaves. Both leaf types intercepted
a greater irradiance during the morning than at midday. Sub-horizontal juvenile leaves intercepted 22% more irradiance than
vertical adult leaves during the middle of the day. The amphistomatal and isobilateral adult leaves intercepted sunlight equally
on both leaf surfaces. Stomatal conductance was variable during the period of measurement but was similar for the Tasmanian
juvenile (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 juvenile leaves would confer a growth advantage to saplings and
regenerating canopies. Reduced light interception and leaf temperature of vertical adult E. globulus leaves would assist in water conservation, particularly at high solar angles.
Keywords:
azimuth, leaf angle, leaf structure, Myrtaceae, ontogeny, temperature.
