Gao Guang, Liu Yameng, Li Xinshu, Feng Zhihua, Xu Juntian
Marine Resources Development Institute of Jiangsu, Huaihai Institute of Technology, Lianyungang, China.
PLoS One. 2016 Dec 29;11(12):e0169040. doi: 10.1371/journal.pone.0169040. eCollection 2016.
Ulva is the dominant genus in the green tide events and is considered to have efficient CO2 concentrating mechanisms (CCMs). However, little is understood regarding the impacts of ocean acidification on the CCMs of Ulva and the consequences of thalli's acclimation to ocean acidification in terms of responding to environmental factors. Here, we grew a cosmopolitan green alga, Ulva linza at ambient (LC) and elevated (HC) CO2 levels and investigated the alteration of CCMs in U. linza grown at HC and its responses to the changed seawater carbon chemistry and light intensity. The inhibitors experiment for photosynthetic inorganic carbon utilization demonstrated that acidic compartments, extracellular carbonic anhydrase (CA) and intracellular CA worked together in the thalli grown at LC and the acquisition of exogenous carbon source in the thalli could be attributed to the collaboration of acidic compartments and extracellular CA. Contrastingly, when U. linza was grown at HC, extracellular CA was completely inhibited, acidic compartments and intracellular CA were also down-regulated to different extents and thus the acquisition of exogenous carbon source solely relied on acidic compartments. The down-regulated CCMs in U. linza did not affect its responses to changes of seawater carbon chemistry but led to a decrease of net photosynthetic rate when thalli were exposed to increased light intensity. This decrease could be attributed to photodamage caused by the combination of the saved energy due to the down-regulated CCMs and high light intensity. Our findings suggest future ocean acidification might impose depressing effects on green tide events when combined with increased light exposure.
石莼是绿潮事件中的优势属，被认为具有高效的二氧化碳浓缩机制（CCM）。然而，关于海洋酸化对石莼CCM的影响以及藻体在适应海洋酸化以应对环境因素方面的后果，我们了解得还很少。在此，我们在环境（LC）和升高（HC）的二氧化碳水平下培养了一种世界性绿藻——石莼，并研究了在HC条件下生长的石莼中CCM的变化及其对海水碳化学和光照强度变化的响应。光合无机碳利用的抑制剂实验表明，在LC条件下生长的藻体中，酸性区室、胞外碳酸酐酶（CA）和胞内CA共同发挥作用，藻体中外源碳源的获取可归因于酸性区室和胞外CA的协同作用。相反，当石莼在HC条件下生长时，胞外CA被完全抑制，酸性区室和胞内CA也不同程度地下调，因此外源碳源的获取仅依赖于酸性区室。石莼中下调的CCM并未影响其对海水碳化学变化的响应，但当藻体暴露于增加的光照强度时，会导致净光合速率下降。这种下降可归因于下调的CCM节省的能量与高光强共同作用导致的光损伤。我们的研究结果表明，未来海洋酸化与增加的光照暴露相结合时，可能会对绿潮事件产生抑制作用。
