Résumé
Maximum assimilation rate under saturating light level, leaf nitrogen and chlorophyll content and specific
leaf mass were measured in forest plants grown under a range of canopy openness. Seedlings from three tree species
co-occurring in damar agroforest (Sumatra) were examined: Shorea javanica, Lansium domesticum and Cinnamomum
porrectum. A shrub species, Piper hispidum, growing in a different location was also investigated. All species showed
pronounced differences in maximum photosynthetic potential when grown under different canopy openness. All tree
seedlings showed an increase in maximum assimilation rate (Amax) with canopy openness (CO) until a certain threshold was reached. This saturation threshold varied between species. A steady increase in the maximum assimilation
rate over the entire range of canopy openness explored was found only for Piper. Correlation between leaf nitrogen
content and Amax was usually highest when expressed on a per unit area basis. However the overall correlation was
poor whether expressed per unit mass or per unit area when all species were pooled together questioning the universality of the relationship between both quantities. Potential photosynthetic nitrogen use efficiency, defined as the amount
of CO2 uptake per unit leaf nitrogen under saturating light level, was highest in Cinnamomum, supposedly the most
light-demanding species, and lowest in Lansium, the understorey specialist.