IN SEARCH OF A PHYSIOLOGICAL BASIS FOR COVARIATIONS IN LIGHT-LIMITED AND LIGHT-SATURATED PHOTOSYNTHESIS

• Published in: Journal of phycology 2004-02, Vol.40 (1), p.4-25
• Main Authors: Behrenfeld, Michael J., Prasil, Ondrej, Babin, Marcel, Bruyant, Flavienne
• Format: Article
• Language: English
• Subjects: Algae; photosynthesis-irradiance relationships; physiology; phytoplankton; productivity
• ISSN: 0022-3646; 1529-8817
• DOI: 10.1046/j.1529-8817.2004.03083.x

The photosynthesis-irradiance (PE) relationship links indices of phytoplankton biomass (e.g. chl) to rates of primary production. The PE curve can be characterized by two variables: the light-limited slope ( alpha super(b)) and the light-saturated rate (P super(b) sub(max)) of photosynthesis. Variability in PE curves can be separated into two categories: that associated with changes in the light saturation index, E sub(k) (=P super(b) sub(max)/ alpha super(b)) and that associated with parallel changes in alpha super(b)and P super(b) sub(max) (i.e. no change in E sub(k)). The former group we refer to as 'E sub(k)-dependent' variability, and it results predominantly from photoacclimation (i.e. physiological adjustments in response to changing light). The latter group we refer to as 'E sub(k)-independent' variability, and its physiological basis is unknown. Here, we provide the first review of the sporadic field and laboratory reports of E sub(k)-independent variability, and then from a stepwise analysis of potential mechanisms we propose that this important yet largely neglected phenomenon results from growth rate-dependent variability in the metabolic processing of photosynthetically generated reductants (and generally not from changes in the oxygen-evolving PSII complexes). Specifically, we suggest that as growth rates decrease (e.g. due to nutrient stress), reductants are increasingly used for simple ATP generation through a fast (