Interactive effects of increased temperature, elevated pCO2and different nitrogen sources on the coccolithophore Gephyrocapsaoceanica

Abstract

As a widespread phytoplankton species, the coccolithophore Gephyrocapsaoceanica has a significant impact on the global biogeochemical cycle through calcium carbonate precipitation and photosynthesis. As global change continues, marine phytoplankton will experience alterations in multiple parameters, including temperature, pH, CO2, and nitrogen sources, and the interactive effects of these variables should be examined to understand how marine organisms will respond to global change. Here, we show that the specific growth rate of G. oceanica is reduced by elevated CO2 (1000 μatm) in NO-3-grown cells, while it is increased by high CO2 in NH+4-grown ones. This difference was related to intracellular metabolic regulation, with decreased cellular particulate organic carbon and particulate organic nitrogen (PON) content in the NO-3 and high CO2 condition compared to the low CO2 condition. In contrast, no significant difference was found between the high and low CO2 levels in NH+4 cultures (p > 0.05). The temperature increase from 20°C to 25°C increased the PON production rate, and the enhancement was more prominent in NH+4 cultures. Enhanced or inhibited particulate inorganic carbon production rate in cells supplied with NH+4 relative to NO-3 was observed, depending on the temperature and CO2 condition. These results suggest that a greater disruption of the organic carbon pump can be expected in response to the combined effects of increased NH+4 /NO-3 3 ratio, temperature, and CO2 level in the oceans of the future. Additional experiments conducted under nutrient limitation conditions are needed before we can extrapolate our findings to the global oceans.