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Aquatic Microbial Ecology

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AME 50:301-311 (2008)  -  DOI:

Coupling between Photosystem II electron transport and carbon fixation in microphytobenthos

E. P. Morris1,2, R. M. Forster1,3, J. Peene1, J. C. Kromkamp1,*

1Netherlands Institute of Ecology (NIOO-KNAW), Centre for Estuarine and Marine Ecology, Korringaweg 7, 4401 NT, Yerseke, The Netherlands
2Present address: Departamento de Biología (Área de Ecología), Facultad de Ciencias del Mar y Ambientales, Universidad de Cádiz, Puerto Real S/N, 11510 Cádiz, Spain
3Present address: Centre for Environment, Fisheries and Aquaculture Science, Lowesoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR3 3OH, UK
*Corresponding author. Email:

ABSTRACT: Photosynthetic parameters of a microphytobenthic (MPB) biofilm grown in a tidal mesocosm were measured on undisturbed sediment using variable fluorescence-based measurements of electron transport rate (ETR), as well as by ETR and 14C assimilation measurements in optically thin suspensions of algal cells. Absorption cross-sections of the MPB suspensions were quantified using the quantitative filter technique and by reconstruction using HPLC-derived pigment concentrations. Photosynthetic parameters derived by the 3 methods were compared on 3 days, representing different biofilm growth/[chl a] conditions, at the start, middle and end of the daytime tidal emersion. Comparisons of ETR and radioisotope-derived photosynthetic parameters measured on optically thin suspensions were not significantly different, confirming that with an appropriate estimation of the irradiance absorbed by Photosystem II (PSII), under optically well-defined conditions, variable fluorescence is a reliable measure of MPB photosynthetic rates. In contrast, significant differences of up to 60% were observed between the maximum photosynthetic capacity (PBmax) measured on undisturbed sediment and in suspensions. These differences were observed at high [chl a] (coinciding with low growth rates) towards the end of emersion periods. Comparison of the effective quantum efficiency (ΔF/Fm’) at the highest light steps of photosynthetic-irradiance (P-E) curves suggested that the overestimation was due to the poor definition of the complex sediment optics, which interacted presumably with photo-taxis and/or single species migrations. Definition of the optics within undisturbed sediments, particularly considering the complex effects of migration, is a serious challenge, limiting the application of variable fluorescence techniques in situ on undisturbed sediments.

KEY WORDS: Variable fluorescence · 14C uptake · Microphytobenthos · Maximum photosynthetic capacity · Maximum quantum yield of photosynthesis · Sediment · Absorption cross-section · PAM fluorescence

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Cite this article as: Morris EP, Forster RM, Peene J, Kromkamp JC (2008) Coupling between Photosystem II electron transport and carbon fixation in microphytobenthos. Aquat Microb Ecol 50:301-311.

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