Macronutrient uptake and carotenoid/chlorophyll a ratio in the dinoflagellate Amphidinium carteri Hulburt, cultured under different nutrient and light conditions

Abstract

Population growth, macronutrient (NO3 -, PO4 3-) uptake and carotenoids/chlorophyll a ratio we determined in Amphidinium carteri Hulburt, cultured under conditions of continuous light (50, 150, 300 and 750 µmol quanta m-2 s-1 ) and three nutrient concentrations NaNO3/NaH2PO4 at 441.5/18.1 µM (low) 883/36.3 µM (medium) and 1766/72.6 µM (high). Both nutrient and irradiance had a significant effect (p < 0.05) on cellular abundance during the period of culture, except for the fourth and seventh day for nutrients (p > 0.05). In cultures under low nutrient condition, NO3 - and PO4 3- were almost depleted by the fifth day and in cultures with medium nutrient this condition occurred in the sixth day; whereas, at high nutrient condition the nutrients were not depleted. We concluded that A. carteri had higher growth rates and nutrient consumption at 300 µmol quanta m-2 s-1 during the first five days and in general the effect of nutrients on the pigment ratios was not significant (p > 0.05). However, the average peridinin/Chla ratio decreased up to 72% from the lowest and the highest irradiance. The opposite was observed for the average of diadinoxanthin/Chla ratio that increased almost two-fold, and the averages dinoxanthin and diatoxanthin to Chla ratios that increased from low to high irradiances. The average diatoxanthin/Chla ratio at 750 µmol quanta m-2 s-1 increased up to 2.7-fold from the exponential to the stationary phase only in the low and medium nutrient concentration. Likewise, the average peridinin, dinoxanthin and diatoxanthin to Chla ratios were not significantly different at 50 and 150 µmol quanta m-2 s-1 . These results indicate important changes in average carotenoids/Chla ratios in A. carteri cultured under different irradiances.