Abstract
To explain the process of CO2 and H2O diffusion between air and plant, analysis was made using a data set concerned with diurnal and seasonal variation of transpiration and net CO2, assimilation rate on leaves of three evergreen broad-leaved trees (Quercus glauca, Cinnarnornum carnphora and Pasania edulis).The observation results about the pattern of diurnal and seasonal change are as follows:(1) Diurnal variation: the pattern of transpiration rate had the peak about at noon, whereas the pattern of net CO2 assimilation rate had the peak in the morning.(2) Seasonal variation: bigger seasonal variation in transpiration rate compared with net CO2 assimilation rate were observed.(3) Water-use efficiency: the values are higher in the morning or in winter than in the afternoon or in summer.Two parameters, stomatal conductance and internal conductance, were used to explain the observation results.From this analysis it is shown quantitatively that stomatal conductance is not the single physiological component deciding CO2 flux and the influence of internal conductance is not negligible. Moreover, it could be explained by analyzing water-use efficiency which environmental and plant factor mainly caused the differences of the pattern of the diurnal and seasonal variation between transpiration rate and net CO2 assimilation rate.
