Using combined measurements of gas exchange and chlorophyll fluorescence to estimate parameters of a biochemical C3 photosynthesis model: a critical appraisal and a new integrated approach applied to leaves in a wheat (Triticum aestivum) canopy

Abstract

We appraised the literature and described an approach to estimate the parameters of the Farquhar, von Caemmerer and Berry model using measured CO 2 assimilation rate (A) and photosystem II (PSII) electron transport efficiency (Φ2). The approach uses curve fitting to data of A and Φ2 at various levels of incident irradiance (Iinc), intercellular CO 2 (Ci) and O 2. Estimated parameters include day respiration (Rd), conversion efficiency of Iinc into linear electron transport of PSII under limiting light [κ2(LL)], electron transport capacity (Jmax), curvature factor (θ) for the non‐rectangular hyperbolic response of electron flux to Iinc, ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) CO 2/O 2 specificity (Sc/o), Rubisco carboxylation capacity (Vcmax), rate of triose phosphate utilization (Tp) and mesophyll conductance (gm). The method is used to analyse combined gas exchange and chlorophyll fluorescence measurements on leaves of various ages and positions in wheat plants grown at two nitrogen levels. Estimated Sc/o (25 °C) was 3.13 mbar µ bar−1; Rd was lower than respiration in the dark; Jmax was lower and θ was higher at 2% than at 21% O 2; κ2(LL), Vcmax, Jmax and Tp correlated to leaf nitrogen content; and gm decreased with increasing Ci and with decreasing Iinc. Based on the parameter estimates, we surmised that there was some alternative electron transport.