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Growth-compensating phenomena in continuous cultures of Dunaliella tertiolecta limited simultaneously by light and nitrate
Sciandra, A.; Gostan, J.; Collos, Y.; Descolas-Gros, C.; Le Boulanger, C.; Martin-Jézéquel, V.; Denis, M.; Lefèvre, D.; Copin-Montégut, G.; Avril, B. (1997). Growth-compensating phenomena in continuous cultures of Dunaliella tertiolecta limited simultaneously by light and nitrate. Limnol. Oceanogr. 42(6): 1325-1339
In: Limnology and Oceanography. American Society of Limnology and Oceanography: Waco, Tex., etc.. ISSN 0024-3590, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Sciandra, A.
  • Gostan, J.
  • Collos, Y.
  • Descolas-Gros, C.
  • Le Boulanger, C.
  • Martin-Jézéquel, V.
  • Denis, M.
  • Lefèvre, D.
  • Copin-Montégut, G.
  • Avril, B., more

Abstract
    Two nitrogen-limited continuous cultures of Dunaliella tertiolecta were grown on light/dark cycles. One was submitted to limiting photon flux density (PFD) and the other to nonlimiting PFD. The growth rate was identical in the two cultures despite the difference in the PFD conditions. Once equilibria were reached in both cultures, the PFD were reversed to simulate a decrease and an increase in light conditions. A large suite of variables was measured to characterize the response of the cells, mainly through the interactions of carbon and nitrogen assimilation pathways. A decrease in irradiance led to a rapid decrease in algal biovolume; the biovolume-based growth rate (mu) descended to levels lower than those estimated for cells of the light-limited culture. An increase in irradiance rapidly led to an increase in mu, which attained values greater than those observed in high-light cells of the other culture before the shift. For the two cultures before and after the shift, cell carbon and cell volume were strongly correlated, showing the same pattern of diel variations.The specific C fixation rates (mu C) of the two cultures before and after the light shift declined significantly during the light periods. Before the Light shift, mu C was paradoxically higher in the low Light culture and could not be predicted only from the light levels. This suggests that some compensatory phenomena may occur during light and nitrogen limitations. Time variations of cell Chl a due to photoacclimation in both cultures were correlated with their N status. Similarly, the regulation of carboxylase activities (Rubisco) by the Light levels was sensitive to the degree of N limitation. We found that nitrogen limitation has an overriding effect compared to Light for the regulation of cell volume, C fixation and respiration rates, Chi a synthesis, electron transport system, and Rubisco activities. In cultures subjected to low irradiance, NO3- uptake rate decreased several hours into the dark phase, suggesting a time lag between the end of photosynthate production and the exhaustion of compounds necessary for dissolved inorganic nitrogen assimilation. The implications of these results concerning phytoplankton growth modeling in a variable environment are important because there are no existing models that correctly integrate the simultaneous effects of light and nitrogen on primary production. It is shown that the effects of these limitations were not additive in the range of light and N limitations tested in this experiment.

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