© 1993 Heron Publishing—Victoria, Canada
Simulated influence of leaf geometry on sunlight interception and photosynthesis in conifer needles
D. N. Jordan and W. K. Smith
Department of Botany, P.O. Box 3165, University Station, University of Wyoming, Laramie, WY 82071-3165, USA / Received September 9, 1992
Summary
The light interception capabilities of individual conifer needles are governed by their cross-sectional geometry and their
orientation to sunlight. Leaf cross sections typical of conifer tree species were modeled to quantify the interception of
direct sunlight over a range of incident light angles. The needle shapes exhibited by Abies nordmanniana Spach, Picea asperata Master, Pinus cembra L., P. monophylla Torr & Frém., and P. sylvestris L. were selected because they are representative of the range of geometric shapes found in conifer tree species. Calculated
light interception values were compared to corresponding predictions for a laminar broadleaf. Estimates of carbon gain were
derived from computed incident light integrated over the leaf cross section and a representative curve of conifer photosynthetic
response to light. Flat leaf cross sections (e.g., Abies nordmanniana) with high surface area to volume ratios (> 6) intercepted more light per unit area at high angles of incidence than thick
leaves. Thick leaves (e.g., Pinus cembra) intercepted more light at low angles of incidence than at high angles of incidence. Needles of Pinus monophylla had no angular dependence for light interception because of their circular cross section. Large differences in estimated
CO2 assimilation occurred among the species, especially when CO2 uptake was expressed on a unit volume basis. A maximum uptake of 67.9 mmol CO2 m–3 s–1 was predicted for A. nordmanniana compared to a minimum of 39.7 mmol m–3 s–1 for P. monophylla. A greater angular dependence occurred for estimates of CO2 uptake than for estimates of light interception.
Keywords:
Abies nordmanniana, conifer needles, leaf geometry, light interception, photosynthesis, Picea asperata, Pinus cembra, Pinus monophylla, Pinus sylvestris.
