Satoru Takanashi

CO 2 exchange in a temperate Japanese cypress forest compared with that in a cool-temperate deciduous broad-leaved forest

To examine the characteristics of carbon exchange in coniferous forests, we analysed the seasonal and diurnal patterns of CO2 exchange, as measured using the eddy covariance method, in a Japanese cypress forest in the Kiryu Experimental Watershed (KEW) in central Japan. The net CO2 exchange data during periods of low-friction velocity conditions and during periods of missing data were interpolated. The daily CO2 uptake was observed throughout the year, with maximum values occurring in early summer. Periods of low carbon uptake were seen in late summer owing to high respiratory CO2 efflux. The diurnal and seasonal patterns of daytime CO2 exchange at KEW were compared with those in a cool-temperate deciduous forest of the Tomakomai Experimental Forest (TOEF) in Japan. The environmental differences between evergreen and deciduous forests affected the seasonal patterns of carbon uptake. Although there were great differences in the mean monthly air temperatures between the sites, the mean monthly daytime carbon uptake was almost equal at both sites during the peak growing period. The carbon-uptake values at the same PAR level were greater before noon than after noon, especially at TOEF, suggesting the stomatal regulation of carbon uptake.

Patterns of root respiration rates and morphological traits in 13 tree species in a tropical forest

The root systems of forest trees are composed of different diameters and heterogeneous physiological traits. However, the pattern of root respiration rates from finer and coarser roots across various tropical species remains unknown. To clarify how respiration is related to the morphological traits of roots, we evaluated specific root respiration and its relationships to mean root diameter (D) of various diameter and root tissue density (RTD; root mass per unit root volume; gcm(-3)) and specific root length (SRL; root length per unit root mass; mg(-1)) of the fine roots among and within 14 trees of 13 species from a primary tropical rainforest in the Pasoh Forest Reserve in Peninsular Malaysia. Coarse root (2-269mm) respiration rates increased with decreasing D, resulting in significant relationships between root respiration and diameter across species. A model based on a radial gradient of respiration rates of coarse roots simulated the exponential decrease in respiration with diameter. The respiration rate of fine roots (<2mm) was much higher and more variable than those of larger diameter roots. For fine roots, the mean respiration rates for each species increased with decreasing D. The respiration rates of fine roots declined markedly with increasing RTD and increased with increasing SRL, which explained a significant portion of the variation in the respiration among the 14 trees from 13 species examined. Our results indicate that coarse root respiration in tree species follows a basic relationship with D across species and that most of the variation in fine root respiration among species is explained by D, RTD and SRL. We found that the relationship between root respiration and morphological traits provides a quantitative basis for separating fine roots from coarse roots and that the pattern holds across different species.

Characteristics of Energy Exchange and Surface Conductance of a Tropical Rain Forest in Peninsular Malaysia

Energy exchange above tropical rain forest was studied using micro-meteorological monitoring from a 52 m tower established in the Pasoh Forest Reserve (Pasoh FR) in Peninsular Malaysia. The meteorological conditions were comparatively drier during the first half of the year and wetter toward the end of the year due to the seasonal variation of rainfall. The five-year observational period from 1995 to 1999 included a low rainfall duration due to the El Nino from 1997 to 1998. The latent heat flux estimated by the Bowen ratio method occupied a dominant portion of the energy exchange even in the driest condition in early 1998. Although evapotranspiration from the dry canopy tended to be smaller in this period than in a wet period during the end of 1998, the surface conductance estimated using the Penman Monteith Equation was consistently controlled by the same function of solar radiation and specific humidity deficit. This suggests the evaporation did not suffer from severe stress of soil water even in the driest condition.

Midday depression of leaf CO2 exchange within the crown of Dipterocarpus sublamellatus in a lowland dipterocarp forest in Peninsular Malaysia

We observed diurnal and seasonal patterns of leaf-scale gas exchange within the crown of a Dipterocarpus sublamellatus Foxw. tree growing in a lowland dipterocarp forest at Pasoh, Peninsular Malaysia. Observations were carried out nine times over 6 years, from September 2002 to December 2007. Observation periods included both wet and mild-dry periods, and natural and saturated photosynthetic photon flux density (PPFD) light conditions. In situ measurements of the diurnal change in net photosynthetic rate and in stomatal conductance were carried out on canopy leaves of a 40-m-tall D. sublamellatus tree, which was accessed from a canopy corridor. A diurnal change in electron transport rate was observed under saturated PPFD conditions. The maximum net assimilation rate was approximately 10 micromol m(-2) s(-1). There was a clear inhibition of the net assimilation rate coupled with stomatal closure after late morning and this inhibition occurred year-round. Although the electron transport rate decreased alongside this inhibition, it sometimes followed on. Numerical analysis showed that the main factor in the inhibition of the net assimilation rate was patchy bimodal stomatal closure, which occurred in both mild-dry and wet periods. The midday depression occurred year-round, though there are fluctuations in soil moisture during the mild-dry and wet periods. The magnitude of the inhibition was not related to soil water content but was related to vapor pressure deficit (VPD): that is, whether the days were sunny and hot or cloudy and cool. On cloudy, cool days in the wet period, the net photosynthesis was only moderately inhibited, but it still decreased in the afternoon and was coupled with patchy stomatal closure, even in quite moderate VPD, leaf temperature and PPFD conditions. Our results suggest that patchy stomatal closure signaled by the increase in VPD, in transpiration and by circadian rhythms, was the key factor in constraining midday leaf gas exchange of the D. sublamellatus canopy leaves.

Vertical variation in leaf gas exchange parameters for a Southeast Asian tropical rainforest in Peninsular Malaysia

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.

Vertical profiles and storage fluxes of CO2, heat and water in a tropical rainforest at Pasoh, Peninsular Malaysia

Ambient CO2 concentration, air temperature and relative humidity were measured intermittently for a 3-year period from the floor to the canopy top of a tropical rainforest in Pasoh, Peninsular Malaysia. Mean diurnal CO2 storage flux (Sc; μmol m-2 s-1) and sensible and latent heat storage fluxes (Qa and Qw; W m-2) ranged from -12.7 to 3.2 μmol m-2 s-1, -15 to 27 W m-2 and -10 to 20 W m-2, respectively. Small differences in diurnal changes were observed in Sc and Qa between the driest and wettest periods. Compared with the ranges of mean diurnal CO2 eddy flux (-14.7 to 4.9 μmol m-2 s-1), sensible eddy flux (-12 to 169 W m-2) and latent eddy flux (0 to 250 W m-2), the contribution of CO2 storage flux was especially large. Comparison with summertime data from a temperate Japanese cypress forest suggested a higher contribution of Sc in the tropical rainforest, probably mainly due to the difference in nighttime friction velocity at the sites. On the other hand, differences in Qa and Qw were smaller than the difference in Sc, probably because of the smaller nighttime sinks/sources of heat and water vapour.

Determination of the gas exchange phenology in an evergreen coniferous forest from 7 years of eddy covariance flux data using an extended big-leaf analysis

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. 2005) inversely from EC flux data over a 7-year period: surface conductance (gc), maximum rate of carboxylation of the “big leaf” (VCMAX), and intercellular CO2 concentration of the “big leaf” (CI). The relationship between gc 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 VCMAX decreased substantially in the winter and was different from that of an evergreen broadleaved forest. A decrease in CI 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.

Observation of the scale of patchy stomatal behavior in leaves of Quercus crispula using an Imaging-PAM chlorophyll fluorometer

Patchy stomatal closure occurs in plants with heterobaric leaves, in which vertical extensions of bundle sheath cells delimit the mesophyll and restrict the diffusion of CO(2). The scale of patchy stomatal behavior was investigated in this study. The distribution of PSII quantum yield (Φ(II)) obtained from chlorophyll fluorescence images was used to evaluate the scale of stomatal patchiness and its relationship with leaf photosynthesis in the sun leaves of 2-year-old saplings of Quercus crispula Blume. Fluorescent patches were observed only during the day with low stomatal conductance. Comparison of numerical simulation of leaf gas exchange and chlorophyll fluorescence images showed that heterogeneous distribution of electron transport rate through PSII (J) was observed following stomatal closure with a bimodal manner under both natural and saturated photosynthetic photon flux densities. Thus, fluorescence patterns can be interpreted in terms of patchy stomatal closure. The mapping of J from chlorophyll fluorescence images showed that the scale of stomatal patchiness was approximately 2.5-fold larger than that of anatomical patches (lamina areas bounded by bundle sheath extensions within lamina). Our results suggest the spatial scale of stomatal patches in Q. crispula leaves.

Effects of soil water status on the spatial variation of carbon dioxide, methane and nitrous oxide fluxes in tropical rain-forest soils in Peninsular Malaysia

To assess the effects of soil water status on the spatial variation in soil carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) fluxes, we examined these gas fluxes and environmental factors in a tropical rain forest in Peninsular Malaysia. Measurements of soil CO 2 , CH 4 and N 2 O fluxes were taken ten, nine, and seven times, respectively over 30 mo at 15 or 39 sampling point within 2-ha plot. Mean (± SE) value of spatially averaged CO 2 flux was 4.70 ± 0.19 μmol CO 2 m −2 s −1 and observed spatial variation in CO 2 flux was negatively related to the volumetric soil water content (VSWC) during the dry period. Over the wet period, extremely high CO 2 emissions were positively correlated with VSWC at some locations, suggesting that no spatial structure of CO 2 flux was because of such hot-spot CO 2 emissions. Flux of CH 4 was usually negative with little variation, with a mean value of –0.49 ± 0.15 mg CH 4 m −2 d −1 , resulting in the soil at our study site functioning as a CH 4 sink. Spatial variation in CH 4 flux was positively related to the VSWC throughout the entire study period (dry and wet). Some CH 4 hot spots were observed during dry periods, probably due to the presence of termites. Mean value of spatially averaged N 2 O flux was 98.9 ± 40.7 μg N m −2 h −1 and N 2 O flux increased markedly during the wet period. Spatially, N 2 O flux was positively related to both the VSWC and the soil N concentration and was higher in wet and anaerobic soils. These findings suggest that denitrification is a major contributor to high soil N 2 O fluxes. Additionally, analysis by adjusting confounding effects of time, location and interaction between time and location in mixed models, VSWC has a negative effect on CO 2 flux and positive effects on CH 4 and N 2 O fluxes. We found that soil water status was related temporally to rainfall and controlled greenhouse gas (GHG) fluxes from the soil at the study site via several biogeochemical processes, including gas diffusion and soil redox conditions. Our results also suggest that considering the biological effects such as decomposer activities may help to explain the complex temporal and spatial patterns in CO 2 and CH 4 fluxes.

Occurrence of stomatal patchiness and its spatial scale in leaves from various sizes of trees distributed in a South-east Asian tropical rainforest in Peninsular Malaysia

In this study, we demonstrated the occurrence of stomatal patchiness and its spatial scale in leaves from various sizes of trees grown in a lowland dipterocarp forest in Peninsular Malaysia. To evaluate the patterns of stomatal behavior, we used three techniques simultaneously to analyze heterobaric or homobaric leaves from five tree species ranging from 0.6 to 31 m in height: (i) diurnal changes in chlorophyll fluorescence imaging, (ii) observation and simulation of leaf gas-exchange rates and (iii) a pressure-infiltration method. Measurements were performed in situ with 1000 or 500 μmol m(-2) s(-1) photosynthetic photon flux density. Diurnal patterns in the spatial distribution of photosynthetic electron transport rate (J) mapped from chlorophyll fluorescence images, a comparison of observed and simulated leaf gas-exchange rates, and the spatial distribution of stomatal apertures obtained from the acid-fuchsin-infiltrated area showed that patchy stomatal closure coupled with severe midday depression of photosynthesis occurred in Neobalanocarpus heimii (King) Ashton, a higher canopy tree with heterobaric leaves due to the higher leaf temperature and vapor pressure deficit. However, subcanopy or understory trees showed uniform stomatal behavior throughout the day, although they also have heterobaric leaves. These results suggest that the occurrence of stomatal patchiness is determined by tree size and/or environmental conditions. The analysis of spatial scale by chlorophyll fluorescence imaging showed that several adjacent anatomical patches (lamina areas bounded by bundle-sheath extensions within the lamina) may co-operate for the distributed patterns of J and stomatal apertures.