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 F_m', 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 F_m'. The technique reveals that whereas F_m' is prone to underestimation, the maximum fluorescence yield following brief cessation of actinic illumination, or F_m", is not. The differential susceptibility of F_m' and F_m" to misestimation renders essential features of photosynthetic regulation, which are governed by coordinated sub-processes of leaf level photosynthesis, subject to misinterpretation.