The mechanism of general flowering in Dipterocarpaceae in the Malay Peninsula is revealed through field survey and meteorological data analyses. The regions of general flowering coincide with those which experienced a low night-time temperature (LNT) c. 2 mo before flowering. This supports the hypothesis that low air temperature induces the development of floral buds of dipterocarps. LNT was found to be caused by radiative cooling during dry spells in winter when the northern subtropical ridge (STR) occasionally migrates southwards with a dry air mass into the equatorial region. LNT events usually occur in La Niña episodes, not in El Niño episodes as believed previously. This is because the southward migration of the STR is associated with the intensification of local meridional Hadley Circulation in the western Pacific, which is strengthened in a La Niña episode. Results suggest that El Niño-like climate change in increased atmospheric carbon dioxide concentrations may be critical for the tropical rain forest biome in south-east Asia.

Summary1 Leaf demography was examined for trees of various heights over a 3.7-year period in a Malaysian rain forest. We compared demography between upper and lower parts of the crown and its relation to height. The results were analysed at the stand level by pooling several trees of various shade-tolerant species, as well as three species for which multiple individuals were sampled. 2 Photon flux density was generally higher in the upper than in the lower crowns. Leaf production rate and leaf loss rate were faster, and number of leaf cohorts and median leaf life span were therefore lower, in the upper crowns of most trees. Faster rates of leaf loss and shorter life spans were associated with increasing height, although leaf production rate was unaffected. 3 Leaf life span and specific leaf area were plastic traits which decreased with height within several shade-tolerant tree species, indicating functional convergence. 4 Vertical distribution of leaf biomass was almost even in the stand. Because leaf life span was shorter in the upper canopy, these leaves contributed most to litter production. The vertical structure of the forest stand was therefore maintained through dynamic processes in trees of various heights over short time-scales.

On a monoaxial erect stem of trees with continuous leafing, the older leaves would be quickly shaded by newer (upper) leaves if the trees did not have any compensating mechanisms to avoid self-shading. We hypothesized that the dynamic adjustment of leaf deployment, by regulating the patterns of leaf growth and by changing leaf orientation as leaves age, is a compensating mechanism. To verify this hypothesis, we analyzed leaf development and crown structure of a Far Eastern tropical pioneer tree species, Macaranga gigantea (Rub. f. et Toll.) M.A., which unfolds huge leaves directly on a monoaxial stem with a short leafing interval. Petioles required more than 90 days for full elongation and the petiole angle (the angle between the petiole axis and the vertical) increased over time. Thus, a series of leaves on a stem progressively increased in petiole length and petiole angle from the youngest to the oldest leaves. This is beneficial because it decreases the degree of self-shading within a crown. A simulation suggested that an average crown for the M. gigantea seedlings, which was constructed using empirically determined morphometric data cannot entirely eliminate self-shading within the crown. But an average crown had a lower degree of self-shading, with less dry mass allocation to the petiole than simulated crowns that were identical to the average crown in all but one respect: they had constant petiole lengths or petiole angles. We conclude that M. gigantea seedlings reduce self-shading by regulating elongation of the petiole and changes in the petiole angle with increasing leaf age.

SUM M A R YFoliar uptake of peroxyacetyl nitrate (PAN) was measured by the gas exchange method on nine herbaceous species. Susceptibility to PAN was also examined in the tested species in order to seek correlations with the uptake rate of PAN. PAN was synthesized by the nitration of peracetic acid in /;-tridecane.Uptake rate of PAN by the leaves was kept at a steady level during the 90 min light period, w-hile in the dark it declined rapidly and reached almost zero within 30-^5 min. This suggests that adsorption of PxiXN on to the surface of the leaves is very small and most of it enters the leaf through open stomata.Among the species tested, sunflower showed the highest rate of PAN uptake, followed by radish, tomato and spinach. Maize and soyahean exhibited the lowest rate. .\ highly significant correlation was observed between the rate of PAN uptake and stomatal conductance among the tested species.Petunia was most susceptible to PAN, followed by radish and tobacco, but maize and peanut were tolerant. There was no significant correlation between the uptake rate of PAN and susceptibility to it among the species. A higher susceptibility of petunia to PAN was not characterized by a higher rate of pollutant uptake. These results show that the main factor determining the differences between species in susceptibility to PAN is not the amount that gains access to the tissues, but some internal metabolic processes.

A structural damage detection method using uncertain frequency response functions (FRFs) is presented in this article. Structural damage is detected from the changes in FRFs from the original intact state. The measurements are always contaminated by noise, and sufficient data are often difficult to obtain; making it difficult to detect damage with a finite number of data. To surmount this, we introduce hypothesis testing based on the bootstrap method to statistically prevent detection errors due to measurement noise. The proposed method iteratively zooms in on the damaged elements by excluding the elements which were assessed as undamaged from among the damage candidates, step by step. The proposed approach was applied to numerical simulations using a 2D frame structure and its efficiency was confirmed.

Allometry of shoot extension units (hereafter termed "current shoots") was analyzed in a Malaysian canopy species, Elateriospermum tapos Bl. (Euphorbiaceae). Changes in current shoot allometry with increasing tree height were related to growth and maintenance of tree crowns. Total biomass, biomass allocation ratio of non-photosynthetic to photosynthetic organs, and wood density of current shoots were unrelated to tree height. However, shoot structure changed with tree height. Compared with short trees, tall trees produced current shoots of the same mass but with thicker and shorter stems. Current shoots with thin and long stems enhanced height growth in short trees, whereas in tall trees, thick and short current shoots may reduce mechanical and hydraulic stresses. Furthermore, compared with short trees, tall trees produced current shoots with more leaves of lower dry mass, smaller area, and smaller specific leaf area (SLA). Short trees adapted to low light flux density by reducing mutual shading with large leaves having a large SLA. In contrast, tall trees reduced mutual shading within a shoot by producing more small leaves in distal than in proximal parts of the shoot stem. The production of a large number of small leaves promoted light penetration into the dense crowns of tall trees. All of these characteristics suggest that the change in current shoot structure with increasing tree height is adaptive in E. tapos, enabling short trees to maximize height growth and tall trees to maximize light capture.

The concentration of ions in plant cells and tissues is an essential factor in determining physiological function. In the present study, we established that concentration gradients of mobile ions exist in both xylem exudates and tissues within a barley (Hordeum vulgare) primary leaf. For K + and NO3 -, ion concentrations generally decreased from the leaf base to the tip in both xylem exudates and tissues. Ion gradients were also found for Pi and Cl -in the xylem. The hydathode strongly absorbed Pi and re-translocated it to the rest of the plant, whereas Cl -was extruded. The ion concentration gradients developed early during leaf growth, increased as the tissue aged and remained under both high and low transpiration conditions. Measurement of the expression profiles of Pi, K + and NO3 -transporters along the longitudinal axis of the leaf revealed that some transporters are more expressed at the hydathode, but for most transporters, there was no significant variation along the leaf. The mechanisms by which longitudinal ion gradients develop in leaves and their physiological functions are discussed.

Leaf phenology was studied in individuals of a canopy species, Elateriospermum tapos (Euphorbiaceae), at various ontogenetic stages, in a Malaysian rain forest. The timing of leaf emergence was not synchronized among sapling individuals, and was not correlated with any meteorological factors of the preceding month. The timing of leaf fall in saplings was positively correlated with net radiation, and maximum and minimum temperature, but negatively correlated with relative humidity the preceding month, although these correlations were weak. The leaf production rate was larger under higher light, but the leaf fall rate was not related to the light regime of the saplings. Thus, leaf production was enhanced by the light availability for each individual, while leaf fall may have been enhanced by drought stress. Non-synchronous leaf production appears to be important for sapling growth, allowing saplings to occupy better-lit space quickly. On the other hand, tall trees showed a clear synchronous leaf-fall pattern, with an annual cycle, and no meteorological factors were correlated with the timing of leaf fall. Mature trees of this species produced flowers simultaneously with new leaves, after shedding their leaves. This suggests that the need to synchronize flowering might be the primary determinant of leaf production phenology in mature individuals.