Studies on Photosynthesis and Primary Production of Rice Plants in Relation to Meteorological Environments

With the purpose to obtain necessary data for constructing a simulation model for photosynthesis and primary production of rice plant in relation to meteorological environments, measurements were made on rice leaves with a leaf chamber method, of the leaf boundary layer resistance (ra) to water vapour transfer in dependence of wind speed and also of stomatal (rs) and mesophyll (rM) diffusive resistances as a function of radiation intensity.ra was found to be proportional to the square root of the effective leaf length along the wind direction, and inversely proportional to the square root of the wind velocity, so that Sherwood number (Sh) was presented in the form: Sh=ARe1/2Sc1/3 with Re and Sc being Reynolds and Schmidt numbers. The proportional constant A appeared to be 0.86-0.91.rM responded almost instantaneously to the suddenly changed radiation levels, while rs took a certain time before it reached a steady-state value. The transitional response pattern in rs to an increased radiation was found to be approximated by a response function of first order lag, while that to a decreased radiation by a function of logistic type. The time constant for the opening response of the stomata appeared to be about 5min. and that for the closing response about 6min.. The steady-state value of rs in the dark was 30-40seccm-1 and it decreased with increasing radiation intensity in a negative exponential fashion. At short-wave radiation intensity of 0.6calcm-2 min-1 (=0.26calcm-2 min-1 in PAR, 400-700nm), rs reached a minimum value of about 1.2sec cm-1·rM also decreased with the increase in radiation up to about 0.8calcm-2 min-1. Under a normal range of the environments, the net photosynthetic rate (Pn) was likely to be restricted more by rM than by rs or ra.A linear relation was found between Pn and the total conductivity for CO2 between outside air and the air in the intercellular spaces, giving a support to the hypothesis (Raschke, 1975) that the stomata stabilize the CO2 concentration in the intercellular spaces at a constant level.