© 2000 Heron Publishing—Victoria, Canada
Influence of light availability on leaf structure and growth of two Eucalyptus globulus ssp. globulus provenances
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
Light availability strongly affects leaf structure of the distinctive ontogenetic leaf forms of Eucalyptus globulus Labill. ssp. globulus. Late-maturing plants from St. Marys, Tasmania and early maturing plants from Wilsons Promontory, Victoria (hereafter referred
to as Wilsons Prom.) were grown for 9 months in 100, 50 or 10% sunlight. Growth, biomass and leaf area were significantly
reduced when plants were grown in 10% sunlight. Provenance differences were minimal despite retention of the juvenile leaf
form by the Tasmanian plants throughout the study. The time taken for initiation of vegetative phase change by the Wilsons
Prom. saplings increased with decreasing light availability, but the nodal position of change on the main stem remained the
same. Both juvenile and adult leaves remained horizontal in low light conditions, but became vertical with high irradiance.
Leaf dimensions changed with ontogenetic development, but were unaffected by light availability. Juvenile leaves retained
a dorsiventral anatomy and adult Wilsons Prom. leaves retained an isobilateral structure despite a tenfold difference in light
availability. Stomatal density and distribution showed ontogenetic and treatment differences. At all irradiances, juvenile
leaves produced the smallest stomata and adult leaves the largest stomata. Amphistomy decreased with decreasing irradiance.
Detrended, correspondence analysis ordination highlighted the structural changes influenced by ontogenetic development and
light availability. Adult leaves had characteristics similar to the xeromorphic, sun-leaf type found in arid, high-light conditions.
Although juvenile leaves had characteristics typical of mesomorphic leaves, several structural features suggest that these
leaves are more sun-adapted than adult leaves.
Keywords:
irradiance, leaf morphology, leaf anatomy, mesophyll, Myrtaceae, ontogeny, sun-shade leaves.
