The Effects of Environmental Factors on the Estimation of Stomatal Diffusion Resistance

A physical mathematical model of water transportation in the soil-plant-atmosphere continuum have been developed recently. To predict daily actual transpiration，much more detailed studies on the behavior of stomata are needed. To make a behavior model of stomatal resistance，concurrent measurements of irradiance，leaf water potential，air temperature，leaf temperature，net radiation，CO₂ concentration， humidity， wind speed and stomatal resistance were obtained in cucumbers under wet soil conditions. The same measurements were made in soybeans under dry and wet conditions. The results indicated that light is likely to have an important role on stomatal behavior under any soil water status. The relationship between stomatal resistance and light fits a hyperbolic curve as shown in Fig. 2. But the duirnal change in leaf water potential did not measurably affect stomatal resistance

Modeling of a Soybean Canopy Structure by the Approximation of a Leaflet into an Ellipsoid for Estimating Direct Solar Radiation Environment

For the detailed analysis of a canopy structure, e.g., solar radiation environment, it is necessary to obtain spatial data related to the leaf position in a canopy. We approximated a leaflet shape into an ellipsoid because, if it is possible, necessary data for determining the spatial position of each leaflet can be obtained by using the manipulator technique, which is used to measure a certain point in space accurately. The coincidence of a soybean leaflet area, which was measured using an area meter, and an ellipsoid area, which was obtained by approximating the maximum width and maximum length of a leaflet to the short axis and long axis of an ellipsoid, respectively, was ascertained in five cultivars of the soybean plant. Then, for a soybean population, the spatial factors of each leaflet were measured with a manipulator, i.e., the spatial position of each leaflet was determined at four points (in three-dimensional spaces) two for the maximum width and two for the maximum length of a leaflet. These data were used for the computer simulation of the canopy structure including the leaf area density in each layer with inclination angles of leaflets and the sunlit area