© 2000 Heron Publishing—Victoria, Canada
Photosynthetic capacity in a central Amazonian rain forest
F. E. Carswell (1), P. Meir (1), E. V. Wandelli (2), L. C. M. Bonates (3), B. Kruijt (1), E. M. Barbosa (3), A. D. Nobre (3), J. Grace (1, 4) and P. G. Jarvis (1)
1. Institute of Ecology and Resource Management, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JU,
United Kingdom / 2. Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Caixa Postal 455, Manaus, AM 69010, Brazil / 3. Instituto Nacional de Pesquisas da Amazônia (INPA), Al. Cosme Ferreira 1756, Manaus, AM 69083, Brazil / 4. Author to whom correspondence should be addressed (fcarswell@srv0.bio.ed.ac.uk) / Received February 2, 1999
Summary
The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model
was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux
density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron
transport (Jmax) and maximum rate of carboxylation by Rubisco (Vcmax) increased significantly with canopy height (P < 0.05). The highest Jmax for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 μmol m–2 s–1 ± 24.2 (SE). The highest Vcmax per canopy height was recorded at the top canopy level (24 m) and was 42.8 ± 5.9 μmol m–2 s–1. Values of Jmax and Vcmax at ground level were 35.8 ± 3.3 and 20.5 ± 1.3 μmol m–2 s–1, espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen
concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area
basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime
leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations
of which may be explained by variations in the environmental variables driving photosynthesis.
Keywords:
canopy height, leaf nitrogen, leaf respiration, photosynthetic photon flux density, vertical profile.
