Differential misestimation of maximum fluorescence yields can confound efforts to optimize photosynthesis.

Efforts to optimize photosynthesis can be informed by measurement of it's underlying and coordinated sub-processes. For decades, non-invasive techniques have been integrated to enable assessment of the coordination that exists within and between the gaseous diffusional, energy productive, and energy consumptive reactions of leaf-level photosynthesis. One of the more prevalent techniques measures chlorophyll a fluorescence using a fluorometer that employes pulsed amplitude modulation (PAM). The maximum fluorescence yield observed under steady-state actinic illumination, or Fm', has been shown to be prone to underestimation. Errors can be propagated to various derivative parameters representative of photosynthetic phenomena that have been identified as targets for photosynthetic optimization. A technique involving a multiphase flash of variable irradiance has been shown to be capable of correcting for underestimation of Fm'. The technique reveals that whereas Fm' is prone to underestimation, the maximum fluorescence yield following brief cessation of actinic illumination, or Fm", is not. The differential susceptibility of Fm' and Fm" to misestimation renders essential features of photosynthetic regulation, which are governed by coordinated sub-processes of leaf level photosynthesis, subject to misinterpretation.