Differences in the Structure and Gas Exchange Physiology of Juvenile and Adult Leaves inMetrosideros excelsa

Abstract

In many plant species, ontogeny is characterized by the production of different leaf forms, but the functional significance of this phenomenon is unclear. In Metrosideros excelsa (Myrtaceae), vegetative phase change is characterized by a transition from glabrous juvenile foliage to adult leaves that possess a dense pubescence on their abaxial surface. We examined the changes to anatomical and physiological leaf characteristics that accompany phase change in this species. There was no consistent change to δ13C during ontogeny in M. excelsa, indicating that the ratio of intercellular to ambient CO2 remained relatively constant. Rates of photosynthesis were lower in adult versus juvenile foliage, apparently because of a reduction in resources invested toward carbon gain. The stomatal conductance to water vapor tended to decline as the development of pubescence progressed but increased in fully pubescent adult leaves. The stomatal limitation to photosynthetic carbon gain (Ls) exceeded 40% in juvenile and tran...