© 2003 Heron Publishing—Victoria, Canada
Three-dimensional lamina architecture alters light-harvesting efficiency in Fagus: a leaf-scale analysis
Stefan Fleck (1), Ülo Niinemets (2, 3), Alessandro Cescatti (4) and John D. Tenhunen (1)
1. Department of Plant Ecology, University of Bayreuth, D-95440 Bayreuth, Germany / 2. Department of Plant Physiology, Institute of Molecular and Cell Biology, University of Tartu, Riia 23, EE 51010 Tartu, Estonia / 3. Author to whom correspondence should be addressed (ylo@zbi.ee) / 4. Centro di Ecologia Alpina, I-38040 Viote del Monte Bondone (TN), Italy / Received July 23, 2002; accepted November 16, 2002; published online May 15, 2003
Summary
Modification of foliage exposition and morphology by seasonal average integrated quantum flux density (Qint) was investigated in the canopies of the shade-tolerant late-successional deciduous tree species Fagus orientalis Lipsky and Fagus sylvatica L. Because the leaves were not entirely flat anywhere in the canopy, the leaf lamina was considered to be three-dimensional
and characterized by the cross-sectional angle between the leaf halves (θ). Both branch and lamina inclination angles with
respect to the horizontal scaled positively with irradiance in the canopy, allowing light to penetrate to deeper canopy horizons.
Lamina cross-sectional angle varied from 170° in the most shaded leaves to 90–100° in leaves in the top of the canopy. Thus,
the degree of leaf rolling increased with increasing Qint, further reducing the light-interception efficiency of the upper-canopy leaves. Simulations of the dependence of foliage
light-interception efficiency on θ demonstrated that decreases in θ primarily reduce the interception efficiency of direct
irradiance, but that diffuse irradiance was equally efficiently intercepted over the entire range of θ values in our study.
Despite strong alteration in foliage light-harvesting capacity within the canopy and greater transmittance of the upper crown
compared with the lower canopy, mean incident irradiances varied more than 20-fold within the canopy, indicating inherent
limitations in light partitioning within the canopy. This extensive canopy light gradient was paralleled by plastic changes
in foliar structure and chemistry. Leaf dry mass per unit area varied 3–4-fold between the canopy top and bottom, providing
an important means of scaling foliage nitrogen contents and photosynthetic capacity per unit area with Qint. Although leaf structure versus light relationships were qualitatively similar in all cases, there were important tree-to-tree
and species-to-species variations, as well as evidence of differences in investments in structural compounds within the leaf
lamina, possibly in response to contrasting leaf water availability in different trees.
Keywords:
acclimation, carbon content, dry mass per unit area, leaf inclination, leaf rolling, light interception, nitrogen content.
