Knowledge of variations in morphophysiological leaf traits with forest height is essential for quantifying carbon and water fluxes from forest ecosystems. Here, we examined changes in leaf traits with forest height in diverse tree species and their role in environmental acclimation in a tropical rain forest in Borneo that does not experience dry spells. Height-related changes in leaf physiological and morphological traits [e.g., maximum photosynthetic rate (Amax), stomatal conductance (gs), dark respiration rate (Rd), carbon isotope ratio (δ(13)C), nitrogen (N) content, and leaf mass per area (LMA)] from understory to emergent trees were investigated in 104 species in 29 families. We found that many leaf area-based physiological traits (e.g., A(max-area), Rd, gs), N, δ(13)C, and LMA increased linearly with tree height, while leaf mass-based physiological traits (e.g., A(max-mass)) only increased slightly. These patterns differed from other biomes such as temperate and tropical dry forests, where trees usually show decreased photosynthetic capacity (e.g., A(max-area), A(max-mass)) with height. Increases in photosynthetic capacity, LMA, and δ(13)C are favored under bright and dry upper canopy conditions with higher photosynthetic productivity and drought tolerance, whereas lower R d and LMA may improve shade tolerance in lower canopy trees. Rapid recovery of leaf midday water potential to theoretical gravity potential during the night supports the idea that the majority of trees do not suffer from strong drought stress. Overall, leaf area-based photosynthetic traits were associated with tree height and the degree of leaf drought stress, even in diverse tropical rain forest trees.

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Climate change exposes vegetation to unusual levels of drought, risking a decline in productivity and an increase in mortality. It still remains unclear how trees and forests respond to such unusual drought, particularly Southeast Asian tropical rain forests. To understand leaf ecophysiological responses of tropical rain forest trees to soil drying, a rainfall exclusion experiment was conducted on mature canopy trees of Dryobalanops aromatica Gaertn.f. (Dipterocarpaceae) for 4 months in an aseasonal tropical rain forest in Sarawak, Malaysia. The rainfall was intercepted by using a soft vinyl chloride sheet. We compared the three control and three treatment trees with respect to leaf water use at the top of the crown, including stomatal conductance (gsmax), photosynthesis (Amax), leaf water potential (predawn: Ψpre; midday: Ψmid), leaf water potential at turgor loss point (πtlp), osmotic potential at full turgor (π100) and a bulk modulus of elasticity (ε). Measurements were taken using tree-tower and canopy-crane systems. During the experiment, the treatment trees suffered drought stress without evidence of canopy dieback in comparison with the control trees; e.g., Ψpre and Ψmid decreased with soil drying. Minimum values of Ψmid in the treatment trees decreased during the experiment, and were lower than πtlp in the control trees. However, the treatment trees also decreased their πtlp by osmotic adjustment, and the values were lower than the minimum values of their Ψmid. In addition, the treatment trees maintained gs and Amax especially in the morning, though at midday, values decreased to half those of the control trees. Decreasing leaf water potential by osmotic adjustment to maintain gs and Amax under soil drying in treatment trees was considered to represent anisohydric behavior. These results suggest that D. aromatica may have high leaf adaptability to drought by regulating leaf water consumption and maintaining turgor pressure to improve its leaf water relations.

Molecular selective adsorption of alkylphenols and alkylanilines onto n-alkyl grafted MCM-41 with different alkyl chain lengths and Al contents was studied. Octyl groups gave better adsorbent performance than pentyl and dodecyl groups. Nitrogen and water adsorption isotherms revealed that the octyl-grafted sample has a large volume of strongly hydrophobic nanospaces between the grafted alkyl chains. Octyl-grafted MCM-41 adsorbed alkylphenols from aqueous solutions with high molecular selectivity: Nonylphenol, an endocrine disrupter, is efficiently removed by adsorption onto n-octyl grafted MCM-41, while adsorption of t-amylphenol is small and that of phenol is undetectable. Comparison of molecular selectivities for alkylphenols and alkylanilines reveals that hydrophilic and hydrophobic groups on molecules independently affect the selectivity. Infrared spectra of n-heptylaniline captured in the adsorbent show that the amino groups are strongly hydrogen-bonded to silanol groups on the inorganic pore walls: The molecules fit into the organic-inorganic nanostructure, interacting with the inorganic walls as well as the organic moiety. Since the amounts of Al that could be doped into MCM-41 were much lower than the adsorption amounts of the 4-nonylphenol and 4-n-heptylaniline, changes in the adsorption amounts due to the formation of acidic sites by Al doping could not be clearly observed. It was concluded that a large volume of highly hydrophobic nanospaces surrounded by ionic inorganic walls was important for efficient adsorption of these molecules.