The linear relationship between the amount of absorbed radiation and dry matter production by crop communities has long been known, and the proportionality constant between them is known as the radiation use efficiency (RUE). To analyze and predict crop production using RUE, the assumption is often made that RUE is not sensitive to radiation intensity and that dry matter production rate (DMPR) is a linear function of radiation intensity.
However, there is evidence in opposition to this assumption, including reports of increasing RUE in shade tests, and hyperbolic response of photosynthetic rate to radiation intensity. The following model was developed and used to analyze the response of DMPR and RUE to daily radiation R_S:
DMPR=DMPR_max(R_S)*g(α)
where DMPR_max (R_S) is the DMPR of a hypothetical soybean community absorbing all radiation, and g(α) represents the effect of radiation absorptivity (α). A hyperbolic curve and a straight line were employed for DMPR_max (R_S) and g (α), respectively. Field experimental data including shade tests were used to determine the parameters for the modet. Two sets of parameters were required to cover the entire experimental period. DMPR_max (R_S) had an apparent curvilinear relationship with R_S. The model successfully described dry matter production under successive low radiation conditions, which could not be estimated by a model with RUE insensitive to radiation.

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Methane flux from rice paddies and methane concentration in soil water at rice paddies were measured weekly through rice growing season of 4 years from 1991 through 1994. Methane flux and methane concentration in the soil water changed through each growing season as well documented by many researchers. In addition, the seasonal patterns of change, as well as total methane emission from rice paddy, varied year to year. The seasonal change and its difference among years were not completely explained with air temperature nor soil temperature. However, assuming that methane emission from rice paddy is driven by diffusion through rice plants, four year data showed that the conductance of rice plants for methane diffusion had wide ranges, and suggested that the conductance was highly dependent on air temperature or soil temperature.

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An environmental control system for measuring net photosynthetic and transpiration rates was constructed to study the feasibility of growing plants under hypobaric condition in order to achieve crop production for a controlled ecological life support system (CELSS) in space. The total pressure of the system's assimilation chamber was reduced to 10kPa, with the rates for spinach and maize plants being measured under total air pressures of 10, 40, 70, and 100kPa at the same CO₂ partial pressure condition. Photosynthetic rates of spinach and maize increased until a total pressure of 10kPa. The rate of increase in the photosynthetic rate under low total pressures was distinctive in maize. In addition, the rate of increase was found to be affected by the CO₂ gas diffusion rate. Photosynthesis is considered to be enhanced by a decrease in boundary layer resistance and stomatal resistance to CO₂ transfer due to an increase in the CO₂ diffusion coefficient. The transpiration rate of spinach slightly increased under low total pressures, whereas that of maize also increased, though much less; both plants had lower rates than those simulated using water vapor diffusion theory.

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The flowering dates of Japanese apricot trees (Prunus mume) at 15 meteorological stations in western Japan are estimated, considering processes both of rest breaking and developing of flower bud. As the basis of estimation, accumulation model using an exponential function of daily mean temperature, so called DTS (the number of days transformed to standard temperature) method, is used for expressing development of flower bud. In this study, it is assumed that flower bud with more advanced rest break obtains greater responsiveness to DTS value. The degree of rest break on each day is quantified as the accumulations of values computed by another exponential function of hourly chilling temperature, and expressed in an index ranged from 0 to 1. Daily DTS value multiplied by the index of degree of rest break is accumulated, and the date, on which its accumulations reach to their mean value required for flowering, is determined as the estimated flowering date.
Due to estimate flowering date accurately, it is necessary to determine the most suitable combination of three parameters in the exponential function of chilling temperature at each station. These parameters represent the point when chilling temperature starts to affect in breaking the rest of flower bud, the optimum temperature to break the rest and the point when rest completes, respectively. Most suitable combination of parameters for each station shows that the rest break of flower bud initiates in late-October and almost completes during the period since late-Novemver until mid-December.
By taking account of the process of rest break into the estimation of flowering date using DTS-method, the part of errors attributed by yearly variation in the succession of rest break process is decreased considerably. The root mean square errors in estimations with corrections considering rest break processes fall within the range of 5-10 days, whereas those without corrections correspond to the range of 7-12 days. Estimation methods with considerations of rest break processes generally account for 70-90% of the variances in actual flowering dates of Japanese apricot.

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A sampling system based on the relaxed eddy accumulation method for continuous trace gas flux measurement was developed. The system consists of a sonic anemometer, a Teflon diaphragm pump, delay circuits, and a differential gas analyzer. Test measurements for the CO₂ flux were carried out over a coniferous forest and a paddy field. The empirical coefficient was determined by comparing with the fluxes measured by the eddy correlation method. This coefficient may be considered practically as a constant (0.57).

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We compared the variability of stomatal conductance between adaxial and abaxial surfaces of maize leaf in different environmental conditions, and addressed stomatal response to environmental factors, such as soil moisture.
The stomatal conductance (G) for each of adaxial (g_std) and abaxial (g_stb) surfaces and both surfaces combined (G_st) of a leaf varied significantly during the measurement. Diurnal changes of g_std, g_stb and G_st were similar showing either unimodal, bimodal, or fluctuating patterns which depended on the environmental regimes of the measurement days. The g_stb was larger than g_std, ratio (α) of g_stb to g_std was not constant, the α varied with change in the environmental conditions during the measurement. Meanwhile, the stomatal conductance (g_std) (Z_S), g_stb (Z_S), G_st (Z_S) in different leaf positions (Z_S, distance from the top of stem) on the stem decreased from upper leaf to lower leaf with quadratic functions, but the ratio of stomatal conductance on the two surfaces (α) in different leaf positions on the stem showed no specific pattern of changes.
Effect of soil water content (θ_S, on mass basis) on the stomatal conductance (G) was expressed as G=G_Max(1-θ_S0/θ_S), where G represented either g_std, g_stb, or G_st; G_Max was the maximum of G; θ_S0 was the soil water content when G=0. The relationships between the daytime average of the ratio α and the average photosynthetic photon flux density, saturation deficit and air temperature were expressed by quadratic functions, but the relationship between the average α and the mean of soil water content on mass basis was linear.

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An experiment was conducted to find out the characteristics of CO₂ flux in a mangrove forest of Thailand during the rainy season. The relaxed eddy accumulation method was applied to the measurement of the CO₂ flux over the forest. The CO₂ flux increased with solar radiation, and the daytime downward CO₂ flux was -0.5-1.0mg m^-2s^-1 for the global radiation 400-800Wm^-2, which is about the same magnitude as the typical values obtained in other tropical or temperate forests. The soil respiration was an order of magnitude smaller in the mangrove forest compared to other forests.

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[in Japanese]

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