© 2005 Heron Publishing—Victoria, Canada
Ontogenetic transition of leaf physiology and anatomy from seedlings to mature trees of a rain forest pioneer tree, Macaranga gigantea
Atsushi Ishida (1, 2), Kenich Yazaki (1) and Ang Lai Hoe (3)
1. Department of Plant Ecology, Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki 305-8687, Japan / 2. Corresponding author (atto@ffpri.affrc.go.jp) / 3. Forest Research Institute Malaysia (FRIM), Kepong 52109, Kuala Lumpur, Malaysia / Received April 21, 2004; accepted November 20, 2004; published online March 1, 2005
Summary
In a field study, we compared anatomy and diurnal gas exchange and chlorophyll fluorescence in sunlit mature leaves of Macaranga gigantea (Reichb. f. and Zoll.) Muell. seedlings, saplings, an adult tree and suckers originating from stumps. We tested the hypothesis
that the pattern of resource use shifts across various life stages with ontogenetic changes in leaf anatomy and physiology.
Among leaves of different developmental stages, seedling leaves were the smallest and thinnest, whereas adult tree leaves
were the largest and thickest, and the air space within the lamina was largest in seedling leaves and smallest in adult tree
leaves. Photosynthetic nitrogen-use efficiency (PNUE) was higher in seedling and sapling leaves than in adult tree leaves.
Mean PNUE in seedling leaves was 1.6 times that in adult tree leaves. Nevertheless, among the developmental stages, net photosynthetic
rate (Pn) per unit leaf area was lowest in seedling leaves because they have the lowest nitrogen (N) content per unit leaf area. In
situ water vapor stomatal conductance (gs) at a given leaf-to-air vapor pressure deficit was highest in sapling leaves, suggesting that they have a high hydraulic
efficiency per unit leaf area. Among developmental stages, intrinsic water-use efficiency (Pn/gs) and photochemical capacity of photosystem II were lowest in seedling leaves. Sapling leaves had the highest N concentration
and Pn per unit dry mass and the highest gs, indicating that the gradual transition from the seedling stage to the sapling stage is accompanied by an accumulation of
N in plant bodies and the development of hydraulic systems to counteract unfavorable environmental stresses. The properties
of adult tree leaves (low PNUE, high carbon:N ratio, small and dense cells and thick lamina) indicate that, during the transition
from the sapling stage to the adult tree stage, the priority of resource use in leaves gradually shifts from enhancement of
photosynthetic performance to defense against herbivory and mechanical damage. Leaf morphology and physiology were coordinated
with the differences in resource use at each life stage.
Keywords:
A
mes/A, C:N ratio, hydraulic efficiency, leaf gas exchange, LMA, ontogeny, photosynthetic nitrogen use efficiency, plant size, vessel
diameter.
