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AME 29:287-296 (2002)
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Abstract
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Light and temperature acclimation of Rhodomonas salina (Cryptophyceae): photosynthetic performance
Astrid Hammer1,*, Rhena Schumann1, Hendrik Schubert2
1University of Rostock, Department of Life Sciences, Institute of Aquatic Ecology, Albert-Einstein-Str. 3, 18051 Rostock, Germany
2University of Greifswald, Institute of Ecology, Grimmer Str. 88, 17487 Greifswald, Germany
*E-mail: astrid.hammer@stud.uni-rostock.de
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ABSTRACT: Blooms of phototrophic cryptophytes have been observed in the highly eutrophic estuarine Darss-Zingst Bodden Chain (DZBC), Germany, during prolonged periods of light limitation due to ice and snow covering. The present study analyses possible
mechanisms by which Rhodomonas salina, as a surrogate for bloom forming DZBC cryptophytes, maintains large densities during these low light/low temperature conditions. Growth, photosynthetic activity and pigment content were examined under 16
combinations of temperature (5 to 20°C) and irradiance (10 to 150 µmol photons m-2 s-1) under nutrient-saturated conditions in a seawater-based medium. R. salina was tested for its capacity to photoacclimate to different light
intensities in relation to temperature by calculating the photoadaptive index Ek (light saturation point of photosynthesis, Pmax/a). Pmax, the maximum photosynthesis rate
and a, the efficiency of light utilisation at limited light intensities remained unchanged with respect to irradiance for every temperature tested. Consequently Ek, the irradiance at which photosynthesis rate
ceased to be light-limited was constant (mean 49 µmol photons m-2 s-1) within the chosen range of irradiances. This indicated that R. salina failed to adapt to down-shift changes in the light regime, at least in terms of
photosynthetic parameters. Pigmentation analyses supported these results showing no acclimation of pigment ratios with regard to growth irradiance for a particular temperature. The calculated irradiance needed for 0 net photosynthesis
(Ec) was about 26 µmol photons m-2 s-1 and did not show any significant variation in light or temperature. The failure of R. salina to respond to down-shift changes in the light regime did not result,
however, in a reduction in growth at low irradiances (10 µmol photons m-2 s-1). Judging from these results, R. salina seems to pursue an alternative strategy to capture energy under low light conditions which we hypothesise to
be uptake of dissolved organic carbon from the seawater-based medium. Follow-up research will concentrate on the relative contribution of heterotrophy to the overall nutrition of R. salina under white ice covering.
KEY WORDS: Bloom · Cryptophytes · Rhodomonas salina · Ice · Photosynthesis · Photoacclimation
Full text in pdf format
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Published in AME Vol.
29, No. 3
(2002) on October 23
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2002
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