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We defined gas exchange phenology as the seasonality of the gas exchange characteristics of a forest canopy, and investigated how the gas exchange phenology could be directly detected from an eddy covariance (EC) dataset and its influence on the canopy fluxes within an evergreen Japanese cypress forest. For the detection of gas exchange phenology, we derived three bulk parameters of the extended big-leaf model (Kosugi et al. ) inversely from EC flux data over a 7-year period: surface conductance ( g), maximum rate of carboxylation of the 'big leaf' ( V), and intercellular CO concentration of the 'big leaf' ( C). The relationship between g and the vapor pressure deficit declined in winter and spring. The relationship between the daily ecosystem respiration and air temperature was greater in the spring than in the other seasons. The temperature dependence curve of V decreased substantially in the winter and was different from that of an evergreen broadleaved forest. A decrease in C was occasionally coupled with the decrease in canopy gross primary production during April and August, indicating that stomatal closure was responsible for a decline in canopy photosynthesis. Gas exchange phenology should be quantified when understanding the determining factors of the seasonality of canopy fluxes at evergreen coniferous forests. [ABSTRACT FROM AUTHOR]

Vertical variation in leaf gas exchange characteristics of trees grown in a lowland dipterocarp forest in Peninsular Malaysia was investigated. Maximum net photosynthetic rate, stomatal conductance, and electron transport rate of leaves at the upper canopy, lower canopy, and forest floor were studied in situ with saturated condition photosynthetic photon flux density. The dark respiration rate of leaves at the various heights was also studied. Relationships among gas exchange characteristics, and also with nitrogen content per unit leaf area and leaf dry matter per area were clearly detected, forming general equations representing the vertical profile of several important parameters related to gas exchange. Numerical analysis revealed that the vertical distribution of gas exchange parameters was well determined showing both larger carbon gain for the whole canopy and at the same time positive carbon gain for the leaves of the lowest layer. For correct estimation of gas exchange at both leaf and canopy scales using multi-layer models, it is essential to consider the vertical distribution of gas exchange parameters with proper scaling coefficients. [ABSTRACT FROM AUTHOR]

We investigated effects of heterogeneous stomatal behavior on diurnal patterns of leaf gas exchange in 10 tree species. Observations were made in middle and upper canopy layers of potted tropical rainforest trees in a nursery at the Forest Research Institute Malaysia. Measurements were taken from 29 January to 3 February 2010. We measured in situ diurnal changes in net photosynthetic rate and stomatal conductance in three leaves of each species under natural light. In both top-canopy and sub-canopy species, midday depression of net assimilation rate occurred in late morning. Numerical analysis showed that patchy bimodal stomatal behavior occurred only during midday depression, suggesting that the distribution pattern of stomatal apertures (either uniform or non-uniform stomatal behavior) varies flexibly within single days. Direct observation of stomatal aperture using Suzuki's Universal Micro-Printing (SUMP) method demonstrated midday patchy stomatal closure that fits a bimodal pattern in Shorea leprosula Miq., Shorea macrantha Brandis. and Dipterocarpus tempehes V.Sl. Inhibition of net assimilation rate and stomatal conductance appears to be a response to changes in vapor pressure deficit (VPD). Variable stomatal closure with increasing VPD is a mechanism used by a range of species to prevent excess water loss from leaves through evapotranspiration (viz., inhibition of midday leaf gas exchange). Bimodal stomatal closure may occur among adjacent stomata within a single patch, rather than among patches on a single leaf. Our results suggest the occurrence of patches at several scales within single leaves. Further analysis should consider variable spatial scales in heterogeneous stomatal behavior between and within patches and within single leaves. [ABSTRACT FROM AUTHOR]

Abstract: The spatial distribution of throughfall in a tropical rainforest in Peninsular Malaysia was evaluated using 100 bucket raingauges placed along a line as well as two large raingauges (collection areas of 9.58 and 7.08m2). Throughfall was clearly large in a treefall gap although it was not significantly different between a typical old-growth area with big trees and another area without big trees. A cyclic variation, the scale of which was 10–15m, was detected in the entire forest through Fourier analysis, and this scale roughly corresponded to the index of canopy cover openness. The observations gave the spatial mean value of throughfall with enough accuracy considering that the distribution of throughfall in the forest was controlled by different scale effects consisting of the size of disturbance areas such as gaps as well as the size of individual canopies. [Copyright &y& Elsevier]