Model forms for triose phosphate utilization-limited photosynthetic rates: implications for estimation of photorespiratory carbon export and the contribution of mesophyll conductance to photosynthesis

Leaf photosynthesis is believed to be determined by three major limiting rates. Compared with the first two limitations set by Rubisco activity and electron transport, respectively, the third limiting process—triose phosphate utilization (TPU)—has received less attention. However, the importance of the limitation set by TPU in whole-plant physiology and crop yield determination has been demonstrated recently (Zhou et al. 2023; Ma et al. 2024). Yet, with progressive comprehension of the TPU-limited rate, the corresponding photosynthetic model equation has undergone several rounds of updating. Herein, the far-reaching consequences of adopting one widely used and three newly updated model forms in estimating relevant photosynthetic parameters are assessed. The results suggested that it is time to shift from the widely used model form to one of the newly updated model forms for the purpose of accuracy as well as simplicity in describing the TPU-limited photosynthetic rate in the context of designing crop ideotypes and modelling vegetation systems.