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Abstract
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 fluores- cence 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-amplitude- modulation and fluorescence induction kinetics—and the interpretation of important variables that reflect changes of photosynthesis and physiological status of microalgal cultures. In particu- lar, 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 9 th International GAP workshop held at the University of Malaga in September 2012.
Highlights
Microalgal cultureMicroalgae — i.e. microscopic prokaryotic cyanobacteria and eukaryotic algae — represent important primary producers in nature and form the basis of the food chain in aquatic environments
In exemplary experiments with microalgal model strains Chlorella (Chlorophyceae) and Trachydiscus (Eustigmatophyceae) we have demonstrated typical records and their interpretation under various culture conditions as related to physiological status and growth
We show a comparison of exemplary fluorescence induction kinetics of various microalgal strains which reflect their physiological features and photosynthetic activity (Fig. 4)
Summary
Microalgae — i.e. microscopic prokaryotic cyanobacteria and eukaryotic algae — represent important primary producers in nature and form the basis of the food chain in aquatic environments. Their substantial benefits over plants are based on their short life. Two basic approaches to mass production are used: one applies to cultivation in open reservoirs (with direct contact between the microalgal culture and the environment), while the other involves closed or semi-closed vessels called photobioreactors (for a recent review, see Grobbelaar 2009, Zittelli et al 2013). For the closed/semi-closed systems a variety of photobioreactors (with either natural or artificial illumination) exists, consisting of glass or transparent plastic tubes, columns or panels, positioned horizontally or vertically, arranged as serpentine loops, flexible coils, a series of panels or column gardens, in which the microalgal suspension is circulated
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