Vertical profiles in a Brunei rain forest: II. Leaf characteristics of Dryobalanops lanceolata

We investigated a range of morphological and ecophysiological characteristics of Dryobalanops lanceolata leaves occupying different vertical positions in a Brunei tropical rain forest. Characteristics were examined in understory leaves and in leaves at five heights within a tree canopy. Differences in all variables existed in the vertical profile as a whole, though low statistical power often prevented the discrimination between leaves at particular heights. Compared with understory leaves, those in the top canopy (31 m) had higher leaf mass area (LMA), and thickness of leaf, adaxial epidermis and palisade layers. Trends in the vertical profile were apparent for stomatal density and LMA (increasing with height) and driptip length (decreasing). Vertical differences in leaf nitrogen were probably due to high values in the mid-canopy. Height differences in net assimilation rate (A) during morning and mid-day were presumably the result of higher A in the upper canopy. Differences in stomatal conductance (g_s) within the profile probably resulted from higher mid-canopy g_s. We attributed vertical differences in leaf water potential (ψ) during the morning and mid-day to the higher ψ in understory leaves. We accepted the hypothesis that differences in leaf characteristics for a single species occur within the vertical profile, and are probably a function of microclimate and/or the plant's developmental stage. We rejected the hypothesis that distinct leaf characteristics exist at different height positions within the canopy, although vertical trends were apparent for some morphological and ecophysiological parameters.