© 1996 Heron Publishing—Victoria, Canada
Shade-shoot structure, photosynthetic performance in the field, and photosynthetic capacity of evergreen conifers
Jerry W. Leverenz (1, 2)
1. Department of Ecology and Environmental Sciences, Swedish University of Agricultural Sciences, Box 7072, S-750 07 Uppsala,
Sweden / 2. The Arboretum, The Royal Veterinary and Agricultural University, Kirkegaardsvej 3A, DK2970 Hoersholm, Denmark / Received March 2, 1995
Summary
Shoot structure can be quantified as the ratio of maximum shoot silhouette area to maximum leaf silhouette (projected) area
(Rmax). I have used published studies on the effects of shade-shoot structure on photosynthetic production of evergreen conifer
stands to test the hypothesis that the lower crown of stands of species with a high Rmax contributes significantly to photosynthetic production. Pruning studies were found inadequate to test this hypothesis rigorously.
Eight studies that used cuvettes to measure photosynthetic production in different crown layers are reviewed. Of six studies
on species with Rmax values larger than 0.7, five found significant rates of photosynthesis in the lower half of the crowns. In contrast, pines,
which have a low Rmax and a low leaf area index (≥ 3.5), had low rates of photosynthesis in the lowest crown zone. In field-grown shoots of all
species examined, photosynthetic capacity was negatively related to Rmax.
Keywords:
field photosynthesis, leaf silhouette area, photosynthetic production, shoot silhouette area.
