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.
Light‐saturated photosynthesis (Pmax) of Emiliania huxleyi (Lohmann) Hay et Mohler is known to be carbonlimited at natural concentrations of dissolved inorganic carbon (DIC). In the present study, light‐limited and light‐saturated photosynthetic rates of E. huxleyi were studied at three concentrations of DIC (2.4, 7.4, and 12.4 mM) for high‐calcite (Cin/Ctot=0.48) and low‐calcite (Cin/Ctot=0.08) cells of the same strain. The photosynthetic efficiency (α) and the maximum quantum yield (θmax)A increased by more than a factor of 2 from the lowest to the highest DIC level. Pmax a, and θmax were always higher for the high‐calcite than for the low‐calcite cells at identical DIC levels. This may indicate that the calcifcation process acts as an extra supplier of CO2 for photosynthesis making the CO2 shortage at natural DIC levels a little smaller for high‐calcite than for low‐calcite E. huxleyi. A dependency of θmax on DIC has not previously been shown for marine phytoplankton. θmax is a key parameter in recent biooptical models of phytoplankton productivity, and the results from the present study are therefore important for modeling the productivity of E. huxleyi.
The efficiency of carbon assimilation in Daphnia magna was estimated as a function of the 14C‐labeling time of the food alga Scenedesmus acutus. The assimilation efficiency of 14C was up to 24% higher at low labeling times (≤ 1.4 generations) (P < 0.05) than at high labeling times (≥ 4.2 generations). In uniformly labeled cells the assimilation efficiency in D. magna was 71 ± 2% SE. Variation in the assimilation efficiency with labeling time is associated with change in the relative distribution of 14C among the different cell compartments in the food alga. Uniform labeling of algae is achieved effectively via exponential growth over several generations in batch cultures from sparse inocula.
Abstract. Mussels (Mytilus edulis) were exposed to the algae Alexandrium ostenfeldii, Chrysochromulina polylepis, Gyrodinium aureolum, Gymnodinium galatheanum and
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