Lochocki, E. B.; McGrath, J. M.

The 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. The model\'s equations are not written consistently across publications, and a common variant is to use the minimum of assimilation rates rather than the minimum of carboxylation rates. This variant, which we call the \"min-A variant,\" makes different predictions than the original FvCB model, 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 model\'s 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.