GROWTH, DARK RESPIRATION AND PHOTOSYNTHETIC PARAMETERS OF THE COCCOLITHOPHORID EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE) ACCLIMATED TO DIFFERENT DAY LENGTH‐IRRADIANCE COMBINATIONS¹

Abstract

Growth, dark respiration rate, Photosynthetic parameters, and chemical composition were determined f m Emiliania huxleyi (Lohmann) Hay et M o h h acclimated to different combinations of day bngth (12, 18, 24 h) and irradiance (30, 100, 200, 800 pmol.m-2.s-'). Specific growth rate (p, day-') and carbon-spec@ dark respiration rate (rdc, day-') were independent of day length, but increased signzficantly with increasing irradiance. The photosynthetic parameters depended on the initial acclimation day bngth and iwadiance: Chlorophyll a-specif c maximum photosynthetic rate (P,nn) increased up to threefold with decreasing day bngth and twofold with increasing iwadiance. The maximum light utilization coeficient (an) and maximum quantum yield (4,J increased up to threefold with decreasing day length. a# increased almost fourfold with decreasing iwadiance, whereas & was independent of iwadiance. Literature data f m phytoplankton indicate that PmB consistently increases with increasing irradiance, and day bngth-iwadiance responses of an and 4m are species spec;@. Results from the present experiment and other studies indicate that i f day length-irradiance variability in the photosynthetic parameters are neglected, this may cause an over-or underestimation up to a factor of two in the photosynthetic rate estimation based on these parameters.

Comparison of photosynthetic responses in diploid and haploid life-cycle phases of Emiliania huxleyi (Prymnesiophyceae)

“…The fact that E k was similar to the culture irradiance level in all of our experiments indicates that the cultures were well acclimated to the light conditions. Under broadly similar conditions of temperature, irradiance/photoperiod, nutrients and specific growth rate, our results for the diploid C-cell stage of E. huxleyi are broadly comparable with those of Nielsen (1997). P chl a max and E k were lower in our study (396 compared to 435 μmol O 2 mg chl a -1 h -1 , and 108 compared to 153 μmol photons m -2 s -1 , respectively) and α chl a was higher (3.8 compared to 2.84 μmol O 2 mg chl a -1 h -1 [μmol photons m -2 s] -1 ).…”

“…Within species, photosynthetic parameters are acclimation dependent, i.e. they vary with environmental factors such as nutrients, dissolved organic carbon, temperature and daily irradiance (Nielsen 1997). Comparing the range of values of photosynthetic parameters for a species in the literature may provide some idea of the reliability of each set of results, but direct comparisons between the values reported in different studies can only be made when culture conditions are very similar.…”

Responses ofEmiliania huxleyi(Prymnesiophyceae) to step changes in photon flux density

“…This research complements earlier studies of the steady-state acclimation of the photosynthetic apparatus of E. huxleyi grown over a range of PFDs (Nielsen, 1997;Harris et al, 2005;Suggett et al 2007) by documenting the rate of response of E. huxleyi to reciprocal shifts between low and high PFD. We provide observations of growth rate, biomass (C, N, protein, RNA), pigment content, light absorption, photosynthetic electron transfer rates based on pulse amplitude modulated fluorescence, rbcL gene expression and ribulose bisphosphate carboxylase-oxygenase (RuBisCO) protein abundance.…”

“…If these ratios are independent of growth PFD, then P C m should also be independent of growth PFD. This appears to be the case not only for E. huxleyi (Nielsen, 1997), and also for most phytoplankton in nutrientreplete growth (MacIntyre et al, 2002). Thus, maintenance of high P C m in cells acclimated to low light appears to be one of the adaptations of phytoplankton to variability in their light environment caused by vertical mixing.…”

Carbon acquisition of marine phytoplankton: Effect of photoperiod length

“…Nielsen (1997) investigated the influence of daylength on the photosynthesis of Emiliania huxleyi, finding a threefold higher chlorophyll a (Chl a)-specific maximum photosynthetic rate when cells were grown under a cycle of 12 : 12 light : dark (LD) compared with continuous light. Moreover, some microalgae are able to keep their carbon-specific growth rate more or less constant independent of daylength Burkhardt et al 1999;Rost et al 2002), which requires that rates of carbon fixation increase with decreasing photoperiod length.…”