Shining Light into a "Black Box": Essential Rationale Underlying Multiphase Flash Methodology

The world we live in is very fragile. Sustainable food production is increasingly under intense pressure due to changing environmental conditions on many levels. Understanding the complexities of how to optimize food production under increasingly deleterious environmental conditions is dependent upon accurate and detailed analyses of plant productivity from the molecular-to-the-remote scales. One method that can link many of these scales has been around for decades, namely, pulse amplitude modulation (PAM) chlorophyll a fluorescence. This technique is used to measure an assortment of important parameters based on chlorophyll a fluorescence. One of the parameters measured by this method is termed the steady state maximum fluorescence yield ( ${\Phi }_{{\mathrm{Fm}}^{\text{'}}}$ ). This parameter, while extremely informative when used to quantify an assortment of processes of intense scientific interest, is nonetheless subject to intrinsic underestimation. A clever approach has evolved over several decades to more accurately estimate ${\Phi }_{{\mathrm{Fm}}^{\text{'}}}$ . The underlying rationale of the methodology requires a thorough and nuanced explanation, which is lacking in the literature. Herein, we systematically develop the essential rationale for accurately measuring ${\Phi }_{{\mathrm{Fm}}^{\text{'}}}$ based on the latest evolution of this approach, called multiphase flash (MPF) methodology.