Explicit expression of mesophyll conductance in the traditional leaf photosynthesis–transpiration coupled model and its physiological significances

Abstract

Almost all terrestrial biosphere models (TBMs) still assume infinite mesophyll conductance (gm) to estimate photosynthesis and transpiration. This assumption has caused low accuracy of TBMs to predict leaf gas exchange under certain conditions. Here, we developed a photosynthesis-transpiration coupled model that explicitly considers gm and designed an optimized parameterization solution through evaluating four different gm estimation methods in 19 C3 species at 31 experimental treatments. Temperature responses of the maximum carboxylation rate (Vcmax) and the electron transport rate (Jmax) estimated using the Bayesian retrieval algorithm and the Sharkey online calculator and gm temperature response estimated using the chlorophyll fluorescence-gas exchange method and anatomy method predicted leaf gas exchange better. The gm temperature response exhibited activation energy (delta Ha) of 63.13+-36.89 kJ mol-1 and entropy (delta S) of 654.49+-11.36 J K-1 mol-1. The gm optimal temperature (Topt_gm) explained 58% of variations in photosynthesis optimal temperature (ToptA). The gm explicit expression has equally important effects on photosynthesis and transpiration estimations. Results advanced understandings of better representation of plant photosynthesis and transpiration in TBMs.