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 -grown cells, while it is increased by high CO2 in -grown ones. This difference was related to intracellular metabolic regulation, with decreased cellular particulate organic carbon and particulate organic nitrogen (PON) content in the 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 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 cultures. Enhanced or inhibited particulate inorganic carbon production rate in cells supplied with relative to 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 / 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.
Highlights
Coccolithophores are unicellular phytoplankton belonging to Class Prymnesiophyceae [1, 2]
Most studies demonstrated that coccolithophores growth, which is a proxy for microbial reproductive fitness, was inhibited by elevated CO2
In our study, increased CO2 resulted in a lower growth rate in NOÀ3 cultures, which is in line with previous findings, whereas high CO2 enhanced G.oceanica’s growthin NHþ4 cultures
Summary
Coccolithophores are unicellular phytoplankton belonging to Class Prymnesiophyceae [1, 2]. They represent a prominent marine phytoplankton functional group and contribute greatly to the carbon cycle [3]. In addition to fixing CO2 into organic compounds through photosynthesis, these unique eukaryotic microalgae can form calcite scales (coccoliths) through calcification [4]. The ballasting of photosynthetic products by coccoliths can efficiently transport carbon from the photic zone, the calcification process is a net source of CO2 to the environment [5, 6].
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