Test of a simple biochemical model for photosynthesis of maize and soybean leaves

Abstract

An accurate treatment of leaf photosynthesis is an important part of a systems model for crop growth. Results from studies of ribulose bisphosphate carboxylase oxygenase (RuBisCO) kinetics allow the simulation of leaf photosynthesis to be based upon carboxylase-oxygenase activity as influenced by ambient conditions of irradiance, temperature and CO2 concentration. A procedure for simulating this activity was developed as a component of a systems model of crop growth. In this procedure, theoretical equations describing carboxylase-oxygenase activity were combined with quantitative determinations of carboxylase-oxygenase kinetics for maize and soybean in order to estimate assimilation rates for these two species under diverse environmental conditions. Rates of assimilation estimated from this procedure were tested against experimental data under varying environmental conditions. Estimated responses of maize leaf assimilation to CO2, irradiance and temperature were consistent with recorded data over a range of 10-50 μmol m-2 s-1, although assimilation at ambient CO2 and higher irradiances was overestimated by ∼10%. Although the estimated response of soybean leaf assimilation to CO2 and irradiance was consistent with field data over a range of 0-30 μmol m-2 s-1, the compensation concentration was overestimated such that assimilation at higher temperature and O2 was underestimated. The results of this study indicate that the theoretical equations used to describe RuBisCO activity may be used with laboratory determinations of RuBisCO kinetics to estimate assimilation at the leaf level under the range of CO2, irradiance and temperature commonly used in photosynthesis experiments, although some discrepancy with experimentally recorded rates is apparent. While data describing RuBisCO activity for various species is increasing, confirmation of values for quantity and kinetic properties will be required for further model development. The relationship between the light reactions and carboxylation must also be further elucidated before more detailed simulations of leaf photosynthesis can be undertaken. © 1989.