Both temperature and nutrient levels are rising in worldwide ocean ecosystems, and they strongly influence biological responses of phytoplankton. However, few studies have addressed the interactive effects of temperature and nitrogen sources on physiological performance of the coccolithophore Emiliania huxleyi. In this study, we evaluated algal growth, photosynthesis and respiration, elemental composition, enzyme activity, and calcification under a matrix of two temperatures gradients (ambient temperature 20 °C and high temperature 24 °C) and two nitrogen sources (nitrate (NO3-) and ammonium (NH4+)). When the algae was cultured with NO3- medium, high temperature reduced algal photosynthesis and nitrate reductase activity, but it did not change other indicators significantly relative to ambient temperature. In addition, E. huxleyi preferred NO3- as the growth medium, whereas NH4+ had negative effects on physiological parameters. In the NH4+ medium, the growth rate, photosynthesis and photosynthetic rate, nitrate reductase activity, and particulate organic carbon and particulate organic nitrogen production rate of the algae decreased as temperature increased. Conversely, high temperature increased cellular particulate organic carbon, cellular particulate organic nitrogen, and particulate inorganic carbon levels. In summary, our findings indicate that the distribution and abundance of microalgae could be greatly affected under warming ocean temperature and different nutrient conditions.
Keywords: Elevated temperature; Emiliania huxleyi; Global warming; Nitrogen sources; Photosynthesis.
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