Photosynthesis monitoring to optimize growth of microalgal mass cultures: application of chlorophyll fluorescence techniques

Since the mid-1990s, chlorophyll a (chl a) fluorescence measurement has become widespread to monitor photosynthetic performance of microalgal mass cultures. This paper aims to provide practical instructions for microalgal physiologists and biotechnologists on how fluorescence monitoring can be used to explain changes in photosynthetic activity of microalgal mass cultures. Emphasis is placed on the 2 most common fluorescence techniques—pulse-amplitudemodulation and fluorescence induction kinetics—and the interpretation of important variables that reflect changes of photosynthesis and physiological status of microalgal cultures. In particular, consideration is given to problems associated with the estimation of the photochemical yield of photosystem II and its relationship to linear electron transport rate and overall photosynthesis. Emphasis is also given to the applications and limitations of these techniques through several case studies. In model experiments with microalgal cultures, typical records and their interpretation under various culture conditions are illustrated. Changes of photosynthetic activity and selected variables monitored by chl a fluorescence techniques can thus be related to changes of cultivation conditions, physiological status and growth of microalgal cultures for a given microalgal strain and cultivation system. In this way, chl a fluorescence may be used as a rapid screening technique to monitor photosynthetic activity and subsequently to estimate growth rate in both indoor and outdoor studies. This text and results formed the basis of a key lecture at the 9th International GAP workshop held at the University of Málaga in September 2012.