Light intensity and the growth of Eucalyptus seedlings. I. Ontogenetic variation in E. fastigata

Abstract

Morphological and physiological variation associated with ontogenetic development is described for E. fastigata and their significance in ecology is discussed. Juvenile, intermediate, and adult leaf stages are identified. These differ in such morphological characteristics as leaf orientation, shape, thickness, chlorophyll content, and anatomical structure (including size, abundance, and distribution of stomata), all details which, in juvenile and intermediate leaves at least, are modified by the light climate under which the plants are grown. There are also significant physiological differences between juvenile and intermediate growth stages, particularly as concern apical dominance and rates of apparent photosynthesis, and modification of these by light climate. A comparison of juvenile and intermediate leaves shows that the former possess a number of features which should permit them to function better in conditions of low light intensity but, contrary to such expectations, rates of apparent photosynthesis are higher in intermediate leaves. That this is so is, it is suggested, due to differences in photosynthetic enzyme activity, an hypothesis which has not been investigated.