Widely Used Variants of the Farquhar-von-Caemmerer-Berry Model Can Cause Errors in Parameter Estimation

AO_SCPLOWBSTRACTC_SCPLOWThe Farquhar-von-Caemmerer-Berry (FvCB) model is the most widely-used mechanistic model of C3 net CO2 assimilation, and it plays a significant role in plant physiology, ecology, climate science, and Earth system modeling. As use of the model has grown, multiple variants have appeared across publications. Although many of these are commonly used, there has not been a detailed investigation of existing variants and their impacts on results and interpretations. Here we summarize the types of variants and their prevalence in the literature, and we present a comprehensive comparison of differences between them. A key finding is that a common variant that uses the minimum of assimilation rates rather than the minimum of carboxylation rates, which we call the "min-A variant," makes different predictions than the original "min-W variant," yet appears in approximately half of highly-cited publications and software tools that use the FvCB model. Another concern is that although leaf biochemistry restricts the range of CO2 partial pressures where limitations due to triose phosphate utilization (TPU) can occur, this restriction is commonly omitted from the models equations. Among other potential issues, these variations can introduce errors exceeding 20% when estimating photosynthetic parameter values from CO2 response curves. It is therefore important to be aware of this source of error when fitting the model, to avoid using the min-A variant, and to include the biochemically-derived CO2 threshold for TPU limitations. CO_SCPLOWENTRALC_SCPLOW TO_SCPLOWHEMEC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWOFC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWTHEC_SCPLOW MO_SCPLOWANUSCRIPTC_SCPLOWThe Farquhar-von-Caemmerer-Berry model of CO2 assimilation plays a key role in plant research, but many publications use variants of the model that differ from the original and can potentially introduce errors in photosynthetic parameter estimates. NO_SCPLOWOVELC_SCPLOW RO_SCPLOWESULTSC_SCPLOW, IO_SCPLOWDEASC_SCPLOWO_SCPCAP, C_SCPCAPO_SCPLOWORC_SCPLOW MO_SCPLOWETHODSC_SCPLOWUsing a literature survey, FvCB model variants are categorized, and some are found to make contradictory predictions. Comparisons against A-Ci curves show that the "min-W variant" exhibits the best performance, especially at low CO2 concentrations.