TY - JOUR T1 - Deriving <em>C</em><sub>4</sub> photosynthesis parameters by fitting intensive <em>A/C<sub>i</sub></em> curves JF - bioRxiv DO - 10.1101/153072 SP - 153072 AU - Haoran Zhou AU - Erol Akçay AU - Brent Helliker Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/06/21/153072.abstract N2 - Photosynthetic assimilation versus intercellular CO2 response curves (A/Ci) are widely measured to estimate photosynthetic parameters for C3 species; however, few parameters have been reported for C4 because of lacking estimation methods. In the current study, we took the frameworks of widely-used estimation methods for C3 and built estimation tools to fit intensive A/Ci curves (6-8 more sampling points) for C4 based on two different assumptions about photosynthesis models and two fitting pro-cedures with estimation improvements. Five photosynthetic parameters are obtained: maximal Rubisco carboxylation rate (Vcmax), electron transport rate (J), day respiration (Rd), maximal PEPc carboxylation rate (Vpmax) and mesophyll conductance (gm). Simulation tests with random errors, out of sample tests and Chlorophyll fluorescence measurements validated the estimation methods. Sensitivity analysis showed Vcmax, J and Vpmax are robust to variation in the input parameters, while Rd and gm varied. The two photosynthesis model assumptions yielded consistent results, although they are different from each other in whether ATP could freely transport between RuBP regeneration and PEP regeneration processes. For the two fitting procedures, one is preferable (lower estimation error) if additional measurements (e.g. fluorescence) are available, however, the two procedures support each other and we recommend using both to achieve more accurate results.Subject headings: C4, photosynthesis parameters,A/Ci curves, nonlinear curve fitting ER -