Abstract:Ocean acidification caused by the rising atmospheric CO2 concentration has been paid attention worldwide, the response process and mechanism of marine phytoplankton to ocean acidification are still not very clear. In this paper, we studied four kinds of microalgae Chrysophyta: Dicrateria sp., Bacillariophyta: Phaeodactylum tricornutum, Chlorophyta: Chlorella vulgaris and Platymonas subcordiformis to assess the response of microalgae to CO2-driven ocean acidification (the future level of the year 2300), and by the variation of quality and quantity of phytoplankton, to predict the potential influence of future global climate change on secondary consumers. The results indicated that compared with the control group, the average growth rates (μ) of the four kinds of microalgae were promoted by elevated CO2 concentration (P<0.05); for the value of μ, P. subcordiformis was the highest, 13.5% higher than the control group, followed by C. vulgaris (μ=5.9%), and then Dicrateria sp. and P. tricornutum (μ=2.2%). High CO2 concentration could increase carbon content and/or decrease nitrogen or phosphorus content, and then increase C/N or C/P ratio of phytoplankton. However, there were species different, both of the C/N, C/P ratio for P. subcordiformis were significantly increased (P<0.05), and C/P ratio of C. vulgaris and C/N ratio of P. tricornutum were significantly increased (P<0.05). The cellular chlorophyll a contents of C. vulgaris was increased significantly by elevated CO2 concentration. However, there were decreasing trends of the others. The maximal efficiency of PSⅡ in a dark-adapted state (Fv/Fm) of P. tricornutum elevated remarkably in the beginning of the experiment, the initial slope of rapid light curves (α) of Dicrateria sp. improved, non-photochemical quenching (NPQ) decreased significantly, and the maximum relative electron transport rate (rETRmax) of P. tricornutum and P. subcordiformis increased significantly (P<0.05). But high CO2 concentration has no remarkable effect on photochemical quenching (qP) of the four phytoplankton (P>0.05). Therefore, the growth rate of P. subcordiformis, C. vulgaris and P. tricornutum accelerated under the high CO2 concentration, whereas nutrition quality declined. Different kinds of phytoplankton have different responses to ocean acidification, which may change oceanic phytoplankton community structure in the future. In addition, the change of C/N and C/P ratio of phytoplankton could influence the primary consumer, such as zooplankton and filtering shellfish, through the food chain.
