Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.