硅藻作为水域初级生产力的主要贡献者，在全球碳及硅的生物地球化学循环中发挥着重要作用。迄今，海洋酸化对硅藻及其它浮游植物类群影响的报道，大都基于短期实验。短期酸化研究的结果，对理解细胞响应海洋酸化及相关化学变化的过程与机制非常重要。然而，长期适应酸化胁迫的细胞，也许会展示不同的生理学响应。硅藻生长快，种群数量大，因此有可能对海洋酸化产生进化性响应。

高坤山教授课题组以分离于南海的三角褐指藻（Phaeodactylum tricornutum CCMA 106）为研究对象，将其长期（1035天，约1860代）暴露于酸化条件下（1000µatm pCO₂, pH_T:7.70），探讨了其生长及光合生理的变化，并与对照组（400µatm pCO₂, pH_T: 8.02）及短期（10天，约20代）酸化处理（1000µatm pCO₂, pH_T:7.70）的细胞，进行了对比性分析。结果发现，适应海水酸化1860代后，该硅藻细胞粒径变小，生长与光合速率（与对照组相比）明显下降，并伴随着呼吸作用的下调。相反，短期酸化提高了三角褐指藻呼吸速率，对其生长及光合作用无显著影响。该研究表明，硅藻类在长期适应酸化过程中，可能产生进化性的生理学变化。该文章暗示，不同浮游植物类群生理生态特性不同，长期适应酸化的生理学响应也会不同，且响应长期酸化的机制也会不同，需要进一步深化研究。

该研究成果近日以“Decreased photosynthesis and growth with reduced respiration in the model diatom Phaeodactylum tricornutum grown under elevated CO₂ over 1800 generations [长期海水酸化对硅藻（三角褐指藻）生长及光合生理的影响]）”为题，发表在Global Change Biology期刊上。，第一作者为2014级博士生李富田，通讯作者为高坤山教授。

Studies on the long-term responses of marine phytoplankton to ongoing ocean acidification (OA) are appearing rapidly in the literature. However, only a few of these have investigated diatoms, which is disproportionate to their contribution to global primary production. Here we show that a population of the model diatom Phaeodactylum tricornutum, after growing under elevated CO₂(1000 μatm, HCL, pH_T: 7.70) for 1860 generations, showed significant differences in photosynthesis and growth from a population maintained in ambient CO₂ and then transferred to elevated CO₂ for 20 generations (HC). The HCL population had lower mitochondrial respiration, than did the control population maintained in ambient CO₂ (400 μatm, LCL, pH_T: 8.02) for 1860 generations. Although the cells had higher respiratory carbon loss within 20 generations under the elevated CO₂, being consistent to previous findings, they downregulated their respiration to sustain their growth in longer duration under the OA condition. Responses of phytoplankton to OA may depend on the timescale for which they are exposed due to fluctuations in physiological traits over time. This study provides the first evidence that populations of the model species, P. tricornutum, differ phenotypically from each other after having been grown for differing spans of time under OA conditions, suggesting that long-term changes should be measured to understand responses of primary producers to OA, especially in waters with diatom-dominated phytoplankton assemblages.

Reference: Li F, Beardall J, Collins S, Gao K (2016). Decreased photosynthesis and growth with reduced respiration in the model diatom Phaeodactylum tricornutum grown under elevated CO₂ over 1800 generations. Global Change Biology, doi: 10.1111/gcb.13501.

Link to full text: http://onlinelibrary.wiley.com/doi/10.1111/gcb.13501/full.