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

SummaryAlmost 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.In this study, 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.Results indicated that temperature responses of the maximum carboxylation rate (Fcmax) and the electron transport rate (Jmax) estimated by fusing the Bayesian retrieval algorithm and the Sharkey online calculator together with gm temperature response estimated by fusing the chlorophyll fluorescence-gas exchange method and anatomy method predicted leaf gas exchange more accurately. The gm temperature response exhibited activation energy (ΔHa) of 63.13 ± 36.89 kJ mol-1 and entropy (ΔS) 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.