Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi (2005 Bergen) and Coccolithus braarudii (RCC 1200), 2010

The physiological performance of two coccolithophore species,Emiliania huxleyi and Coccolithus braarudii, was investigated during long-term exposure to elevated pCO2 levels. Mono-specific cultures were grown over 152 (E. huxleyi) and 65 (C. braarudii) generations while pCO2 was gradually increased to maximum levels of 1150 ?atm (E. huxleyi) and 930 ?atm (C. braarudii) and kept constant thereafter. Rates of cell growth and cell quotas of particulate organic carbon (POC), particulate inorganic carbon (PIC) and total particulate nitrogen (TPN) were determined repeatedly throughout the incubation period. Increasing pCO2 caused a decrease in cell growth rate of 9% and 29% in E. huxleyi and C. braarudii, respectively. In both species cellular PIC:TPN and PIC:POC ratios decreased in response to rising pCO2, whereas no change was observed in the POC:TPN ratios of E. huxleyi and C. braarudii. These results are consistent with those obtained in shorter-term high CO2exposure experiments following abrupt pertubations of the seawater carbonate system and indicate that for the strains tested here a gradual CO2 increase does not alleviate CO2/pH sensitivity.

本研究针对两种颗石藻（coccolithophore）——艾氏球石藻（Emiliania huxleyi）与布氏球石藻（Coccolithus braarudii）在长期暴露于升高二氧化碳分压（pCO₂）环境下的生理表现展开探究。实验采用单种培养体系，分别让两种藻历经152代（艾氏球石藻）与65代（布氏球石藻）的培养周期，期间逐步将二氧化碳分压提升至最高值1150 μatm（艾氏球石藻）与930 μatm（布氏球石藻），随后维持该分压恒定。在整个培养周期内，研究人员定期测定细胞生长速率以及颗粒有机碳（POC）、颗粒无机碳（PIC）与总颗粒态氮（TPN）的细胞配额。二氧化碳分压升高分别导致艾氏球石藻与布氏球石藻的细胞生长速率下降9%与29%。两种藻类的细胞PIC:TPN与PIC:POC比值均随二氧化碳分压升高而降低，但艾氏球石藻与布氏球石藻的POC:TPN比值均未出现显著变化。本研究结果与此前通过海水碳酸盐系统突然扰动开展的短期高CO₂暴露实验所得结论一致，表明针对本次试验所用的藻株而言，逐步升高CO₂浓度并不能缓解其对CO₂/pH的敏感性。