An attempt to establish a synthetic model of photosynthesis-transpiration based on stomatal behavior for maize and soybean plants grown in field

A synthetic model of photosynthesis-transpiration was established based on a comprehensive consideration of models of CO2 and H2O fluxes controlled by stomata of plant leaves.The synthetic model was developed by introducing the internal conductance to CO2 assimilation, gic, and the general equation of stomatal conductance model to H2O diffusion, gsw = g0+a1Amf(Ds)/(Cs-Γ), into models of CO2 and H2O diffusion through the plant leaves stomata. In the above expression, g0 and a1 are coefficients, Cs ambient CO2 concentration at leaf surface, Γ CO2 compensation point, and f(Ds) the general function describing the response of stomatal conductance to humidity. Using the data observed in maize (Zea mays L.) and soybean (Glycine max Merr.) plants grown in the field, the parameters in the model were identified, and the applicability of the model was examined. The verification indicated that the developed model could be used to estimate net assimilation rate, transpiration rate, and water use efficiency with a high enough level of precision. The examination also showed that when f(Ds) = hs or f(Ds) = (1+Ds/D0)−1 was employed, the estimation precision of the synthetic model was highest. In the study, the parameter gic was estimated by means of a linear function of QP because it was shown to be mostly correlated with photosynthetic photon flux, QP, among various environmental factors.