CHLOROPHYLL FLUORESCENCE AS A MEASURE OF PHOTOSYNTHETIC CARBON ASSIMILATION

It has long been supposed that there must be an inverse relation between chlorophyll fluorescence and phosynthetic carbon assimilation. Excitation of chlorophyll, by light, initiates the electron transport that drives photosynthesis. Excess excitation energy is dissipated as heat and as light (fluorescence) but, at least in regard to carbon assimilation, the actual fluorescence signal was once regarded as too complex to permit interpretation. More recently, the concept of two major fluorescence-quenching mechanisms and the development of techniques and devices that allow these to be resolved, has advanced understanding. Concepts and procedures based on linear relations between fluorescence parameters and carbon assimilation have allowed good predictions of photosynthetic rates. Here we show that a single curvilinear relation can be derived for several disparate plant species and suggest that this could allow photosynthesis and the effect of light on 'dark respiration' to be measured by non-intrusive fluorescence techniques without recourse to analysis of gaseous exchange between leaf and atmosphere.