Abstract
Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (Jabs). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering–absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with >99% of the absorbed light energy being dissipated as heat and <1% used by photosynthesis at Jabs>700 μmol photon m−2 s−1 (>150 J m−2 s−1). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014−0.047 O2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at Jabs>700 μmol photon m−2 s−1, they reached around 10% of the maximum values at depths 0−0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.
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Acknowledgements
We thank the technicians of the microsensor group for microsensor construction and Paul Faerber, Harald Osmers, Georg Herz and Volker Meyer for their technical support. We thank Dr Henk Jonkers and Prof Friedrich Widdel for fruitful discussions, and Prof Waleed Hamza for his guidance and assistance during sampling. Two anonymous reviewers are specially thanked for their useful comments and suggestions to improve the paper. This study was financially supported by the Max Planck Society (to DB, BBJ and LP), the Yusef Jameel foundation (to MA-N) and the Danish Natural Science Research Council (to MK).
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Al-Najjar, M., de Beer, D., Jørgensen, B. et al. Conversion and conservation of light energy in a photosynthetic microbial mat ecosystem. ISME J 4, 440–449 (2010). https://doi.org/10.1038/ismej.2009.121
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DOI: https://doi.org/10.1038/ismej.2009.121
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