In vivo temperature response functions for leaf steady-state photosynthesis models

Abstract

Predicting environmental responses of leaf photosynthesis is central for modeling changes in the future global carbon cycle and terrestrial biosphere. The steady-state biochemical model of C3 photosynthesis of Farquhar et al. (1980; Planta 149, 78-90) provides a basis for these larger scale predictions; but a weakness as currently parameterized is the inability to predict accurately carbon assimilation over an ecologically significant range of temperatures. The previous parameters were based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Inaccuracies in the functions predicting Rubisco- or RuBP-limited kinetic properties at different temperatures may cause significant error. Both anti-rbcS, for estimating Rubisco-kinetic over a larger range of Ci, and wild-type tobacco, to estimate RuBP regeneration kinetics, were used in this study. The temperature functions of the kinetic properties were estimated in vivo from the rate of CO2 assimilation over a wide range of temperatures, and CO2 and O2 concentrations. The results differed substantially from previously published functions for Rubisco- and RuBP-limited photosynthesis. These new functions were used to predict photosynthesis in lemon and tobacco and found to faithfully mimic the observed pattern of temperature response. Gas-exchange measurements coupled with fluorescence were also made to determine the temperature response of mesophyll conductance for estimating Rubisco kinetics based on CO2 concentrations at the chloroplast level. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10-40 ºC) necessary for predicting carbon uptake by terrestrial C3 systems.