Response of a natural Phytoplankton community from the Qingdao coast (Yellow Sea, China) to variable CO<sub>2</sub> levels over a short-term incubation experiment
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Date
2015Author
Biswas, H.
Jie, J.
Li, Y.
Zhang, G.
Zhu, Z.-Y.
Wu, Y.
Zhang, G.-L.
Li, Y.-W.
Liu, S.M.
Zhang, J.
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Since marine phytoplankton play a vital role in stabilizing earth’s climate by removing significant amount of atmospheric CO<sub>2</sub>, their responses to increasing CO<sub>2</sub> levels are indeed vital to address. The responses of a natural phytoplankton community from the Qingdao coast (NW Yellow Sea, China) was studied under different CO<sub>2</sub> levels in microcosms. HPLC pigment analysis revealed the presence of diatoms as a dominant microalgal group; however, members of chlorophytes, prasinophytes, cryptophytes and cyanophytes were also present. δ<Sup>13</sup>C<sub>POM</sub> values indicated that the phytoplankton community probably utilized bicarbonate ions as dissolved inorganic carbon source through a carbon concentration mechanism (CCM) under low CO<sub>2</sub> levels, and diffusive CO<sub>2</sub> uptake increased upon the increase of external CO<sub>2</sub> levels. Although, considerable increase in phytoplankton biomass was noticed in all CO<sub>2</sub> treatments, CO<sub>2</sub>-induced effects were absent. Higher net nitrogen uptake under low CO<sub>2</sub> levels could be related to the synthesis of CCM components. Flow cytometry analysis showed slight reduction in the abundance of Synechococcus and pico-eukaryotes under the high CO<sub>2</sub> treatments. Diatoms did not show any negative impact in response to increasing CO<sub>2</sub> levels; however, chlorophytes revealed a reverse tend. Heterotrophic bacterial count enhanced with increasing CO<sub>2</sub> levels and indicated higher abundance of labile organic carbon. Thus, the present study indicates that any change in dissolved CO<sub>2</sub> concentrations in this area may affect phytoplankton physiology and community structure and needs further long-term study.
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