The effects of irradiance, temperature, thermal‐ and chilling‐light sensitivities on the photosynthesis of a temperate alga, Sargassum macrocarpum (Fucales) were determined by a pulse amplitude modulation (PAM)‐chlorophyll fluorometer and dissolved oxygen sensors. Oxygenic photosynthesis–irradiance curves at 8, 20, and 28°C revealed that the maximum net photosynthetic rates (NP max) and saturation irradiance were highest at 28°C, and lowest at 8°C. Gross photosynthesis and dark respiration determined over a range of temperatures (8–36°C) at 300 μmol photons m−2 s−1 revealed that the maximum gross photosynthetic rate (GPmax) occurred at 27.8°C, which is consistent with the highest seawater temperature in the southern distributional limit of this species in Japan. Additionally, the maximum quantum yields of photosystem II (F v/F m) during the 72‐h temperature exposures were stable at 8–28°C, but suddenly dropped to zero at higher temperatures, indicative of PSII deactivation. Continuous exposure (12 h) to irradiance of 200 (low) and 1000 (high) μmol photons m−2 s−1 at 8, 20, and 28°C revealed greater declines in their effective quantum yields (Φ PSII) under high irradiance. While Φ PSII under low irradiance were very similar with the initial F v/F m under 20 and 28°C, values rapidly decreased with exposure duration at 8°C. At this temperature, F v/F m did not recover to initial values even after 12 h of dark acclimation. Final F v/F m of alga at 28°C under high irradiance treatment also did not recover, suggesting its sensitivity to photoinhibition at both low and high temperatures. These photosynthetic characteristics reflect both the adaptation of the species to the general environmental conditions, and its ability to acclimate to seasonal changes in seawater temperature within their geographical range of distribution.

中文翻译：

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光合作用活动，包括温带日本褐藻 Sargassum macrocarpum 的热和冷光敏感性

通过脉冲幅度调制 (PAM)-叶绿素荧光计和溶解氧传感器确定辐照度、温度、热和冷光敏感性对温带藻类马尾藻 (Fucales) 光合作用的影响。8、20 和 28°C 下的含氧光合作用-辐照度曲线显示，最大净光合速率 (NP max) 和饱和辐照度在 28°C 时最高，在 8°C 时最低。在 300 μmol 光子 m−2 s−1 的温度范围 (8–36°C) 内测定的总光合作用和暗呼吸显示最大总光合速率 (GPmax) 发生在 27.8°C，这与最高值一致该物种在日本南部分布界限的海水温度。此外，在 72 小时的温度暴露期间，光系统 II (F v/F m) 的最大量子产率稳定在 8-28°C，但在更高的温度下突然下降到零，表明 PSII 失活。在 8、20 和 28°C 下连续暴露（12 小时）200（低）和 1000（高）μmol 光子 m-2 s-1 的辐照度显示在高辐照度下它们的有效量子产率 (Φ PSII) 下降更大. 虽然低辐照度下的 Φ PSII 与 20 和 28°C 下的初始 F v/F m 非常相似，但值随着 8°C 的暴露时间而迅速下降。在这个温度下，即使经过 12 小时的暗适应，F v/F m 也没有恢复到初始值。藻类在 28°C 下在高辐照度处理下的最终 F v/F m 也没有恢复，表明其对低温和高温下的光抑制敏感。