Warming and nutrient limitation are stressors known to weaken the health of microalgae. In situations of stress, access to energy reserves can minimize physiological damage. Because of its widespread requirements in biochemical processes, iron is an important trace metal, especially for photosynthetic organisms. Lowered iron availability in oceans experiencing rising temperatures may contribute to the thermal sensitivity of reef‐building corals, which rely on mutualisms with dinoflagellates to survive. To test the influence of iron concentration on thermal sensitivity, the physiological responses of cultured symbiotic dinoflagellates (genus Breviolum; family Symbiodiniaceae) were evaluated when exposed to increasing temperatures (26 to 30°C) and iron concentrations ranging from replete (500 pM Fe’) to limiting (50 pM Fe’) under a diurnal light cycle with saturating radiance. Declines in photosynthetic efficiency at elevated temperatures indicated sensitivity to heat stress. Furthermore, five times the amount of iron was needed to reach exponential growth during heat stress (50 pM Fe′ at 26–28°C vs. 250 pM Fe′ at 30°C). In treatments where exponential growth was reached, Breviolum psygmophilum grew faster than B.minutum, possibly due to greater cellular contents of iron and other trace metals. The metal composition of B.psygmophilum shifted only at the highest temperature (30°C), whereas changes in B.minutum were observed at lower temperatures (28°C). The influence of iron availability in modulating each alga’s response to thermal stress suggests the importance of trace metals to the health of coral‐algal mutualisms. Ultimately, a greater ability to acquire scarce metals may improve the tolerance of corals to physiological stressors and contribute to the differences in performance associated with hosting one symbiont species over another.

中文翻译：

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铁的可用性调节内共生的鞭毛藻对热应激的反应

变暖和营养限制是已知会削弱微藻健康的压力源。在压力的情况下，获得能量储备可以最大程度地减少生理损伤。由于其在生化过程中的广泛需求，铁是一种重要的痕量金属，尤其是对于光合生物而言。温度升高的海洋中铁的可用性降低，可能会导致造礁珊瑚的热敏感性提高，因为珊瑚需要与鞭毛藻共生才能生存。为了测试铁浓度对热敏感性的影响，培养共生鞭毛鞭毛藻的生物响应（Breviolum属）; 在日照光周期和饱和辐射下，暴露于升高的温度（26至30°C）和铁浓度范围从充足（500 pM Fe'）到极限（50 pM Fe'）的情况下，对Sym科（Symbiodiniaceae）进行了评估。高温下光合作用效率的下降表明对热胁迫敏感。此外，在热应力下达到指数增长所需的铁量是铁的五倍（26–28°C下为50 pM Fe'，而30°C下为250 pM Fe'）。在达到指数增长护理，Breviolum psygmophilum增长速度比乙。藻，可能是由于铁等微量金属的较大的细胞内容物。B的金属组成。嗜热菌B仅在最高温度（30°C）时移动，而B的变化。在较低的温度（28°C）下观察到最小。铁的可利用性在调节每个藻类对热胁迫的响应中的影响表明，微量金属对珊瑚-藻类共生的健康至关重要。最终，获得稀有金属的更大能力可能会提高珊瑚对生理应激源的耐受性，并导致与一种共生物种比另一种共生有关。