CONTROL ID: 1817341

TITLE: Advantages of estimating parameters of photosynthesis model by fitting A-C_i curves at multiple subsaturating light intensities

AUTHORS (FIRST NAME, LAST NAME): Wenting Fu¹, Lianhong Gu², Forrest M Hoffman²

INSTITUTIONS (ALL): 1. University of Texas at Austin, Austin, TX, United States.
2. Oak Ridge National Laboratory , Oak Ridge, TN, United States.

ABSTRACT BODY: The photosynthesis model of Farquhar, von Caemmerer & Berry (1980) is an important tool for predicting the response of plants to climate change. So far, the critical parameters required by the model have been obtained from the leaf-level measurements of gas exchange, namely the net assimilation of CO₂ against intercellular CO₂ concentration (A-C_i) curves, made at saturating light conditions. With such measurements, most points are likely in the Rubisco-limited state for which the model is structurally overparameterized (the model is also overparameterized in the TPU-limited state). In order to reliably estimate photosynthetic parameters, there must be sufficient number of points in the RuBP regeneration-limited state, which has no structural over-parameterization. To improve the accuracy of A-C_i data analysis, we investigate the potential of using multiple A-C_i curves at subsaturating light intensities to generate some important parameter estimates more accurately. Using subsaturating light intensities allow more RuBp regeneration-limited points to be obtained. In this study, simulated examples are used to demonstrate how this method can eliminate the errors of conventional A-C_i curve fitting methods. Some fitted parameters like the photocompensation point and day respiration impose a significant limitation on modeling leaf CO₂ exchange. The multiple A-C_i curves fitting can also improve over the so-called Laisk (1977) method, which was shown by some recent publication to produce incorrect estimates of photocompensation point and day respiration. We also test the approach with actual measurements, along with suggested measurement conditions to constrain measured A-C_i points to maximize the occurrence of RuBP regeneration-limited photosynthesis. Finally, we use our measured gas exchange datasets to quantify the magnitude of resistance of chloroplast and cell wall-plasmalemma and explore the effect of variable mesophyll conductance. The variable mesophyll conductance takes into account the influence of CO₂ from mitochondria, comparing to the commonly used constant value of mesophyll conductance. We show that after considering this effect the other parameters of the photosynthesis model can be re-estimated. Our results indicate that variable mesophyll conductance has most effect on the estimation of the parameter of the maximum electron transport rate (Jmax), but has a negligible impact on the estimated day respiration (Rd) and photocompensation point (<2%).

KEYWORDS: 0428 BIOGEOSCIENCES Carbon cycling.
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CONTACT (NAME ONLY): Wenting Fu
CONTACT (E-MAIL ONLY): wenting076@gmail.com
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