Quantitative expression of mesophyll conductance temperature response in the FvCB model and impacts on plant gas exchange estimations

Abstract

The way of quantitatively expressing mesophyll conductance (gₘ) in the Farquhar-von Caemmerer-Berry (FvCB) photosynthesis model and its impacts on plant gas exchange estimations have not been well explored, primarily due to huge uncertainties in gₘ parameterization. Here, a peaked Arrhenius function to depict gₘ temperature response was introduced into the FvCB model and parameterized through evaluating four different gₘ estimation methods in 19 C₃ species at 31 experimental treatments. Results indicated that the FvCB model without explicitly considering gₘ cannot perform well in eight species/treatments, while the model that considers gₘ estimated by the chlorophyll fluorescence–gas exchange method and biochemical parameters estimated by the Bayesian retrieval algorithm was superior. Overall modeling accuracy was not further ameliorated when taking anatomy-based gₘ into consideration. The increasing Arrhenius function without considering the suboptimal stage of gₘ temperature response caused significant overestimations in photosynthesis under high leaf temperatures by 2–3 folds. The gₘ explicit expression had equally important effects on photosynthesis and transpiration estimations, which disagreed with “the asymmetric effects on photosynthesis and transpiration estimations” hypothesis proposed by Knauer et al. (2020). Literature survey plus our data indicated that observed variations of photosynthesis optimal temperature (TₒₚₜA) were primarily explained by the gₘ optimal temperature (Tₒₚₜ_gₘ) (58%) rather than biochemical limitations, which disagreed with “the JVr biochemical limitations” hypothesis proposed by Kumarathunge et al. (2019).

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