Department of Biology, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan.
J Phycol. 2021 Feb;57(1):3-13. doi: 10.1111/jpy.13078. Epub 2020 Dec 3.
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.
升温以及营养限制是众所周知的会削弱微藻健康的胁迫因子。在胁迫条件下，获取能量储备可以将生理损伤最小化。由于铁在生化过程中有广泛的需求，因此它是一种重要的痕量金属，特别是对光合生物而言。在经历升温的海洋中，铁的可用性降低可能会导致造礁珊瑚对热的敏感性增加，因为珊瑚依赖与甲藻的共生关系来生存。为了检验铁浓度对热敏感性的影响，在一个有昼夜光周期和饱和辐射的环境中，当暴露在逐渐升高的温度（26-30°C）和从充足（500 pM Fe'）到限制（50 pM Fe'）的铁浓度下时，培养共生甲藻（Breviolum 属；Symbiodiniaceae 科）的生理反应被评估。在高温下光合作用效率的下降表明其对热胁迫敏感。此外，在热胁迫下，需要五倍于正常生长所需的铁量才能达到指数增长（26-28°C 时为 50 pM Fe'，而 30°C 时为 250 pM Fe'）。在达到指数增长的处理中，B.psygmophilum 的生长速度比 B.minutum 快，这可能是由于其细胞内铁和其他痕量金属的含量较高。B.psygmophilum 的金属组成仅在最高温度（30°C）下发生变化，而 B.minutum 的变化则发生在较低温度（28°C）下。铁可用性在调节每种藻类对热胁迫的反应中的影响表明，痕量金属对珊瑚-藻类共生关系的健康很重要。最终，获取稀缺金属的能力的提高可能会提高珊瑚对生理胁迫的耐受性，并有助于解释与宿主一种共生体物种相比，另一种共生体物种表现出的差异。
