Sap flow transportation from root to leaf in trees is explained by the cohesion of water molecules pulled up by tension due to transpiration.However, in some species, it has been observed that there can be several minutes to hours of time-lag in sap flow between the crown and the base of the stem.This time lag is assumed to be a proxy for the capacity of water storage to supply water for transpiration.To examine whole-tree water use in relation to internal stem water storage, we measured crown and basal sap flow using hand-made Granier sensors in tropical broadleaf and temperate conifer trees.Measurements on tropical broadleaf trees were conducted at the Pasoh Forest Reserve in Peninsular Malaysia with Dipterocarpus sublamellatus (height = 45 m, DBH = 69 cm) a dominant emergent tree species, and Ptychopyxis caput-medusae (height = 32 m, DBH = 38 cm), a canopy tree adjacent to D. sublamellatus.Measurements on temperate conifers were conducted at the Kiryu Experimental Forest in central Japan with Chamaecyparis obtusa (height = 20 m, DBH = 20 -60 cm), an important plantation tree in Japan.In D. sublamellatus, very narrow time lags between crown and basal sap flows were observed, suggesting internal stem water storage contributed little to daytime whole-tree water use.In P. caput-medusae and C. obtusa, basal sap flow started later than crown sap flow in the morning, suggesting partial reliance on internal stem water storage for daytime whole-tree water use.Additionally, basal sap flow continued until midnight, after the crown sap flow had stopped, indicating refilling of internal stem water storage during the night.

In tropical rainforests the pattern and quantity of rainfall influence various ecosystem functions, as well as forest stand structure by controlling soil water status. In the present study, spatial distribution of volumetric soil water content (VSWC), measured over 1 year, was compared with stand structure in a Southeast Asian tropical rainforest. Forest surface-layer VSWC was determined by the relative elevation and soil physical properties. The patterns of spatial variation in surface-layer VSWC and residual VSWC during dry period suggested that drier surface soil areas had developed forest soil texture with larger pore size. There were no relationships between VSWC and tree mortality or number of trees for all soil layer, but a significant negative relationship was found between surface-layer VSWC and basal area, and thus also biomass. This could be due to the preference of trees for drier surface areas with larger median pore size. The positive relationship between mean diameter at breast height (dbh) and deep layer soil water content might indicate the preference of deep layer water by big trees. On the other hand, the number of trees in Dipterocarpaceae, as well as of emergent species trees, was negatively correlated with SWC in deep soil layer.

We present the temporal variability of the oxygen (delta O-18) and hydrogen (delta H-2) isotope signatures in precipitation at Pasoh Forest Reserve (FR), a tropical rainforest in Peninsular Malaysia. We investigated the daily and seasonal variability of stable isotope signatures in precipitation, particularly in relation to the effects of monsoon seasons, rainfall characteristics and larger scale trends compared with those at nearby Global Network of Isotopes in Precipitation (GNIP) monitoring stations. The isotope signatures did not differ between monsoon seasons but were correlated with amount of rainfall, its intensity and duration. The effect of amount of rainfall on isotope composition was clearly detected and comparable with long-term mean monthly statistics of nearby GNIP stations. Unfortunately the effect was obscured at the daily timescale and, for monthly rainfall, not averaged over the long-term. No large deuterium excess was detected at the daily timescale for small-scale rainfall events. The delta O-18 in precipitation water was more closely correlated with the 60-day antecedent rainfall index than with the amount of rainfall each day. These findings suggested that the isotopic composition in the study area was the result of a rainout on a larger scale in addition to the local scale and specific rain events.

We present the temporal variability of the oxygen (δ 18 O) and hydrogen (δ 2 H) isotope signatures in precipitation at Pasoh Forest Reserve (FR), a tropical rainforest in Peninsular Malaysia.We investigated the daily and seasonal variability of stable isotope signatures in precipitation, particularly in relation to the effects of monsoon seasons, rainfall characteristics and larger scale trends compared with those at nearby Global Network of Isotopes in Precipitation (GNIP) monitoring stations.The isotope signatures did not differ between monsoon seasons but were correlated with amount of rainfall, its intensity and duration.The effect of amount of rainfall on isotope composition was clearly detected and comparable with long-term mean monthly statistics of nearby GNIP stations.Unfortunately the effect was obscured at the daily timescale and, for monthly rainfall, not averaged over the long-term.No large deuterium excess was detected at the daily timescale for small-scale rainfall events.The δ 18 O in precipitation water was more closely correlated with the 60-day antecedent rainfall index than with the amount of rainfall each day.These findings suggested that the isotopic composition in the study area was the result of a rainout on a larger scale in addition to the local scale and specific rain events.

Clarifying variations in soil moisture is an important part of hydrological and ecological studies in tropical rainforests. Volumetric soil water content (VSWC) was measured at depths of 10, 20 and 30 cm at Pasoh Forest Reserve (PFR) in Peninsular Malaysia for 12 years. VSWC ranged from 0.280-0.442 m(3) m(-3) (mean +/- standard error; 0.373 +/- 0.001 m(3) m(-3)) and was affected not only by the south-west and north-east monsoons but also by El Nino and La Nina events. Mean VSWC was high during La Nina events and low during El Nino events. In a normal El Nino/Southern Oscillation (ENSO) phase, VSWC showed both low and high conditions. An antecedent precipitation index (API) was calculated using 20 years of rainfall data. API(90) ranged from 1.2-257.3 mm (25.4 +/- 0.2 mm). The variations in API(90) followed a similar pattern to variations in the VSWC. API(90) can be used to estimate soil moisture conditions as a drought indicator. An API(90) of less than 10 mm lasted more than 14 successive days during the normal ENSO phases when five mass flowerings occurred at PFR from 1995-2014.

To clarify the factors controlling temporal and spatial variations of soil carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) fluxes, we investigated these gas fluxes and environmental factors in a tropical rainforest in Peninsular Malaysia. Temporal variation of CO 2 flux in a 2-ha plot was positively related to soil water condition and rainfall history. Spatially, CO 2 flux was negatively related to soil water condition. When CO 2 flux hotspots were included, no other environmental factors such as soil C or N concentrations showed any significant correlation. Although the larger area sampled in the present study complicates explanations of spatial variation of CO 2 flux, our results support a previously reported bipolar relationship between the temporal and spatial patterns of CO 2 flux and soil water condition observed at the study site in a smaller study plot. Flux of CH 4 was usually negative with little variation, resulting in the soil at our study site functioning as a CH 4 sink. Both temporal and spatial variations of CH 4 flux were positively related to the soil water condition. Soil N concentration was also related to the spatial distribution of CH 4 flux. Some hotspots were observed, probably due to CH 4 production by termites, and these hotspots obscured the relationship between both temporal and spatial variations of CH 4 flux and environmental factors. Temporal variation of N 2 O flux and soil N 2 O concentration was large and significantly related to the soil water condition, or in a strict sense, to rainfall history. Thus, the rainfall pattern controlled wet season N 2 O production in soil and its soil surface flux. Spatially, large N 2 O emissions were detected in wet periods at wetter and anaerobic locations, and were thus determined by soil physical properties. Our results showed that, even in Southeast Asian rainforests where distinct dry and wet seasons do not exist, variation in the soil water condition related to rainfall history controlled the temporal variations of soil CO 2 flux, CH 4 uptake, and N 2 O emission. The soil water condition associated with soil hydraulic properties was also the important controlling factor of the spatial distributions of these gas fluxes.

We separately examined the temporal patterns of root production by Japanese oak (Quercus crispula) and dwarf bamboo (Sasa veitchii), which is a major understory species in cool temperate forests. We grew Japanese oak seedlings and Sasa stocks (i.e., the rhizome and connected culms) in organic-free sand in rhizoboxes and then scanned roots that were visible through the sides of the rhizoboxes to measure the length of each root in images. Japanese oak root production peaked in July, but Sasa root production peaked in both July and October. Soil temperature was highly correlated with root production of Japanese oak, but less so with Sasa root. Leaves of Sasa expanded in late summer, and the photosynthetic rate of Sasa was highest in September, suggesting that the aboveground phenology influences the extensive root production of Sasa in October due to the supply of carbohydrate. These results demonstrate different temporal patterns of root production by Japanese oak seedlings and understory species (Sasa), even under similar environmental conditions.

Evapotranspiration over a Japanese cypress forest was estimated using both the eddy covariance and water budget methods. The long-term water budget revealed that there has been no obvious change in the annual amount of evapotranspiration in this watershed for 33 years despite tree growth, succession, occasional cutting and natural disturbance. Comparison of the eddy covariance method, with a correction for the energy budget, and long-term and short-term water budget methods strongly suggests the validity of the results of both methods and also demonstrates that both the amplitude and characteristics of the seasonal fluctuation of evapotranspiration show no significant interannual differences despite considerable fluctuation in precipitation and hence soil moisture. The three-year average amount of evapotranspiration from the eddy covariance method, with a correction for the energy budget (735mm) were very close to the 33-year average amount of evapotranspiration from the water budget method (749mm).

滋賀県南部桐生水文試験地において2年半にわたり土壌呼吸速度の時空間分布の観測を行った。土壌呼吸速度は, 斜面下部の土壌水分が年間を通じて高い場所において, 斜面上部および中部に比べて低い値を示した。一方で, 各場所での時間変動をみた場合には, 土壌呼吸速度は地温の変動に伴い変動するものの, 乾燥により土壌水分が低下するようなときには土壌呼吸速度の低下がみられた。土壌呼吸速度は, 地温が高くなるにつれて指数関数的に増加し, Q10は, 2.00から2.20の範囲にあった。土壌水分の変動に対しては, 二次式モデルを使用した場合が, 最も適合した。得られた地温, 土壌水分と土壌呼吸速度の関係を用いて, 年間土壌呼吸量の推定を行ったところ, 2003年は692±21, 2004年は716±46gCm-2yr-1と推定された。

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.

Carbon dioxide and sensible and latent heat fluxes over a warm-temperate evergreen broad-leaved forest in central Japan observed for 3.5 years using the eddy covariance method were analysed with an extended big-leaf model. Net ecosystem production (NEP) was estimated after correcting for night-time efflux by using chamber observations of soil and leaf respiration and for day-time CO2 flux by using the light–response curve. Peak CO2 uptake occurred during early summer and autumn; a summer depression and winter uptake were also characteristic of this forest. The estimated NEP showed differences among the years, depending on drought and radiation conditions. The mid-day average of surface conductance was fluctuated between 5 and 10mms−1 during normal years and sometimes decreasing in dry summers. In the wet summer, it increased up to 20mms−1. During the severe and long-term drought, the surface conductance was clearly depressed, suggesting that the surface conductance was strongly influenced by drought. The canopy maximum carboxylation rate (big-leaf VCMAX) was derived from 30min fluxes using the same inversion procedure as used in leaf-level analysis. VCMAX at the normal period was generally explained with one temperature-dependence curve (VCMAX25: 58.4μmolm−2s−1, ΔHa: 32,200Jmol−1) at this warm-temperate evergreen broad-leaved forest. The decline of the normalised VCMAX (VCMAX25) was detected during the severe drought and the expanding period. VCMAX25 did not recover after rain during winter of the year of the severe drought, which suggests that leaf function had suffered severe damage.

Understanding the energy/H2O/CO2 exchange processes of tropical rain forests is very important for evaluating their roles in climate change. We measured sensible heat, latent heat, and CO2 fluxes above a tropical rain forest in Peninsular Malaysia using the eddy covariance method for the year 2003. The average daily sensible and latent heat fluxes were 3.0 and 6.1 MJ, respectively. After considering the calculated heat storage terms, energy budget closure was estimated to be approximately 65%, even during the day. The average daily CO2 flux was -2.1 g C m(-2) in 2003. The average diurnal change of CO2 flux ranged from -18.0 to 10.0 mu mol m(-2) s(-1), and no significant seasonal changes were observed. In the night time, CO2 efflux measured using the eddy covariance method increased with friction velocity, suggesting an underestimation of ecosystem respiration under poor mixing conditions.

ABSTRACTA combined model to simulate CO2 and H2O gas exchange at the leaf scale was parameterized using data obtained from in situ leaf‐scale observations of diurnal and seasonal changes in the CO2 and H2O gas exchange of four temperate deciduous broad‐leaved trees using a porometric method. The model consists of a Ball et al. type stomatal conductance submodel [Ball, Woodrow & Berry, pp. 221–224 in Progress in Photosynthesis Research (ed. I. Biggins), Martinus‐Nijhoff Publishers, Dordrecht, The Netherlands, 1987] and a Farquhar et al. type biochemical submodel of photosynthesis (Farquhar, von Caemmerer & Berry, Planta 149, 78–90, 1980). In these submodels, several parameters were optimized for each tree species as representative of the quantitative characteristics related to gas exchange. The results show that the seasonal physiological changes of Vcmax25 in the biochemical model of photosynthesis should be used to estimate the long‐term CO2 gas exchange. For Rd25 in the biochemical model of photosynthesis and m in the Ball et al. type stomatal conductance model, the difference should be counted during the leaf expansion period.