Resilience to temperature and pH changes in a future climate change scenario in six strains of the polar diatom Fragilariopsis cylindrus@en

The effects of ocean acidification and increased temperature on physiology of six strains of the polar diatom Fragilariopsis cylindrus from Greenland were investigated. Experiments were performed under manipulated pH levels (8.0, 7.7, 7.4, and 7.1) and different temperatures (1, 5, and 8 °C) to simulate changes from present to plausible future levels. Each of the 12 scenarios was run for 7 days, and a significant interaction between temperature and pH on growth was detected. By combining increased temperature and acidification, the two factors counterbalanced each other, and therefore no effect on the growth rates was found. However, the growth rates increased with elevated temperatures by 20-50% depending on the strain. In addition, a general negative effect of increasing acidification on growth was observed. At pH 7.7 and 7.4, the growth response varied considerably among strains. However, a more uniform response was detected at pH 7.1 with most of the strains exhibiting reduced growth rates by 20-37% compared to pH 8.0. It should be emphasized that a significant interaction between temperature and pH was found, meaning that the combination of the two parameters affected growth differently than when considering one at a time. Based on these results, we anticipate that the polar diatom F. cylindrus will be unaffected by changes in temperature and pH within the range expected by the end of the century. In each simulated scenario, the variation in growth rates among the strains was larger than the variation observed due to the whole range of changes in either pH or temperature. Climate change may therefore not affect the species as such, but may lead to changes in the population structure of the species, with the strains exhibiting high phenotypic plasticity, in terms of temperature and pH tolerance towards future conditions, dominating the population.本研究探究了源自格陵兰岛的6株极地硅藻圆柱拟脆杆藻（Fragilariopsis cylindrus）的生理机能对海洋酸化与升温的响应。实验通过设置梯度pH值（8.0、7.7、7.4与7.1）与温度（1、5、8 ℃），模拟当前至未来合理预估的环境变化幅度。12种实验处理组合均持续培养7天，结果检测到温度与pH对该硅藻的生长存在显著交互作用。当升温与酸化胁迫共同存在时，二者的效应会相互抵消，因此未观测到对生长速率的整体影响。不过，不同菌株对升温的响应存在差异，升温可使生长速率提升20%~50%。此外，海洋酸化加剧会对生长产生普遍的抑制效应。在pH 7.7与7.4条件下，不同菌株的生长响应差异显著；但在pH 7.1时，菌株的响应更为统一，多数菌株相较于pH 8.0组的生长速率降低20%~37%。需要特别指出的是，本研究证实温度与pH间存在显著交互作用，即二者的组合对生长的影响，与单独考量任一变量时的效应均存在差异。基于上述结果，我们预计极地硅藻圆柱拟脆杆藻（F. cylindrus）在本世纪末预估的温度与pH变化范围内，不会受到显著负面影响。在每个实验模拟情景中，菌株间的生长速率差异，均大于单一变量pH或温度全范围变化所带来的差异。因此，气候变化或许不会直接威胁该物种种群的存续，但可能会改变其种群结构：那些对未来温度与pH胁迫具备较高表型可塑性的菌株，将在种群中占据主导地位。