Data of photosynthesis and mineralogy of Jania rubens at low pH/high pCO2@en

Corallinales (Rhodophyta) are high Mg-calcite macroalgae and are considered among the most vulnerable organisms to ocean acidification (OA). These sensitive species play fundamental roles in coastal systems as food source and settlement promoters as well as being involved in reef stabilization, and water carbonate balance. At present only a few studies are focused on erect calcifying macroalgae under low pH/high pCO2 and the contrasting results make difficult to predict the ecological consequences of the OA on the coralline algae. In this paper the physiological reasons behind the resistance of Jania rubens, one of the most common calcareous species, to changing ocean pH are analysed. In particular, we studied the photosynthetic and mineralogical response of J. rubens after a three-week transplant in a natural CO2 vent system. The overall results showed that J. rubens could be able to survive under predicted pH conditions even though with a reduced fitness; nevertheless physiological limits prevent the growth and survival of the species at pH 6.7. At low pH (i.e. pH 7.5), the maximum and effective PSII efficiency decreased even if the increase of Rubisco expression suggests a compensation effort of the species to cope with the decreased light-driven products. In these circumstances, a pH-driven bleaching phenomenon was also observed. Even though the photosynthesis decreased at low pH, J. rubens maintained unchanged the mineralogical composition and the carbonate content in the cell wall, suggesting that the calcification process may also have a physiological relevance in addition to a structural and/or a protective role. Further studies will confirm the hypotheses on the functional and evolutionary role of the calcification process in coralline algae and on the ecological consequences of the community composition changes under high pCO2 oceans.珊瑚藻目（Corallinales，红藻门Rhodophyta）为高镁方解石型大型藻类，被认为是对海洋酸化（OA）最敏感的生物类群之一。这些敏感物种在海岸生态系统中发挥着基础生态功能：既是重要的食物来源与附着基促进因子，同时参与珊瑚礁固着与水体碳酸盐平衡调控。目前，针对低pH/高pCO₂环境下直立钙化大型藻类的研究仍较为匮乏，且已有研究结果存在显著分歧，这使得难以准确预测海洋酸化对珊瑚藻类的生态影响。本文围绕朱红镰藻（Jania rubens）——最常见的钙化藻类物种之一——应对海洋pH变化的生理机制展开分析。具体而言，我们通过将朱红镰藻移植至天然CO₂喷口系统中培养三周，探究了其光合生理与矿物学特征的响应规律。整体实验结果表明，尽管适合度有所下降，朱红镰藻仍可在未来预估的海洋pH条件下存活；但在pH 6.7的极端环境下，该物种的生长与存活将受到生理极限的制约。在pH 7.5的低pH环境中，其光系统II（Photosystem II，简称PSII）的最大光化学效率与实际光化学效率均出现下降，尽管核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的表达量有所上调，提示该物种通过补偿机制应对光驱动产物合成量的降低。在此条件下，我们还观测到了pH驱动的藻体白化现象。尽管低pH环境下朱红镰藻的光合能力有所下降，但其细胞壁的矿物组成与碳酸盐含量未发生显著改变，这表明钙化过程除了具备结构与/或保护功能外，还可能具有重要的生理意义。未来的相关研究将进一步验证关于珊瑚藻类钙化过程的功能与进化意义，以及高pCO₂海洋环境下群落组成变化所带来的生态后果的相关假说。