Long-term acclimation to elevated pCO2 alters carbon metabolism and reduces growth in the Antarctic diatom Nitzschia lecointei

Increasing atmospheric CO2 levels are driving changes in the seawater carbonate system, resulting in higher pCO2 and reduced pH (ocean acidification). Many studies on marine organisms have focused on short-term physiological responses to increased pCO2, and few on slow-growing polar organisms with a relative low adaptation potential. In order to recognize the consequences of climate change in biological systems, acclimation and adaptation to new environments are crucial to address. In this study, physiological responses to long-term acclimation (194 days, approx. 60 asexual generations) of three pCO2 levels (280, 390 and 960 µatm) were investigated in the psychrophilic sea ice diatom Nitzschia lecointei. After 147 days, a small reduction in growth was detected at 960 µatm pCO2. Previous short-term experiments have failed to detect altered growth in N. lecointei at high pCO2, which illustrates the importance of experimental duration in studies of climate change. In addition, carbon metabolism was significantly affected by the long-term treatments, resulting in higher cellular release of dissolved organic carbon (DOC). In turn, the release of labile organic carbon stimulated bacterial productivity in this system. We conclude that long-term acclimation to ocean acidification is important for N. lecointei and that carbon overconsumption and DOC exudation may increase in a high-CO2 world.

大气二氧化碳（CO₂）浓度持续升高正驱动海水碳酸盐体系发生变化，致使二氧化碳分压（pCO₂）升高、pH值降低，即海洋酸化（Ocean Acidification）。目前针对海洋生物的多数研究聚焦于生物对升高的pCO₂的短期生理响应，而针对生长缓慢、适应潜力相对较低的极地生物的相关研究则较为匮乏。为厘清气候变化对生物系统的影响，对新环境的驯化与适应是亟需开展的关键研究议题。本研究以嗜冷海冰硅藻莱科因菱形藻（Nitzschia lecointei）为研究对象，探究了其在3种pCO₂水平（280、390与960 µatm）下经过194天（约60个无性世代）长期驯化后的生理响应。实验进行147天后，在960 µatm的pCO₂条件下检测到了小幅的生长抑制。此前的短期实验未能在莱科因菱形藻中观测到高pCO₂条件下的生长变化，这一结果凸显了实验时长在气候变化相关研究中的重要性。此外，碳代谢过程亦受到长期实验处理的显著影响，致使细胞释放的溶解有机碳（DOC）水平升高。相应地，易降解有机碳的释放会提升该系统内的细菌生产力。本研究结论表明，长期驯化以适应海洋酸化对莱科因菱形藻至关重要，且在高CO₂环境下，碳过度消耗与DOC分泌现象可能会愈发显著。