We determined the effect of irradiance and temperature on the photosynthesis of two heteromorphic life‐history stages of an endangered freshwater red alga, Thorea gaudichaudii (Thoreales) by laboratory and field measurements. Net oxygenic photosynthesis–irradiance models of macroscopic and microscopic life‐history stages revealed similar low irradiance‐adapted responses, with a compensation irradiance (Ec) of 6.71 and 2.56 μmol photons m−2 s−1 (4.30–9.13 and 0.13–7.19, 95% Bayesian prediction interval, BPI) and saturating irradiance (Ek) of 26.6 and 30.0 μmol photons m−2 s−1 (19.0–37.4 and 12.1–63.0, BPI), respectively. A temperature‐dependent model of net photosynthesis and dark respiration in macroscopic and microscopic stages also showed similar temperature responses, and the gross photosynthetic rate (GPmax), 3.54 and 6.34 μg O2 gww−1 min−1 (3.10–3.99 and 5.31–8.21, BPI), was highest at 32.1 and 35.7°C (29.8–34.0 and 29.5–48.6, BPI). The maximum quantum yields (F v/F m) in macroscopic and microscopic stages were also similar in response with respect to temperature; however, it was somewhat steady at low temperatures with the highest value of 0.54 and 0.62 (0.54–0.55 and 0.61–0.63, BPI) at 17.8 and 15.0°C (16.7–18.8 and 12.3–17.1, BPI). The effective quantum yield (Φ PSII) in macroscopic and microscopic stages was also negatively correlated with irradiance, which decreased after 12 h of continuous exposure to 50 (low) and 1000 (high) μmol photons m−2 s−1 at 12 and 22°C. Large declines of Φ PSII and subsequent failure of F v/F m recovery were particularly enhanced at high irradiance, signifying photoinhibition. Diurnal change of Φ PSII and incident irradiance of the macroscopic stage under the field measurement revealed the midday depression of Φ PSII; however, there was little direct sunlight due to shading by the trees, and algae were occurring in the shaded locations in the freshwater spring.

中文翻译：

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来自日本的淡水红藻 Thorea gaudichaudii (Thoreales) 的两个异形生活史阶段的光合活动对辐照度和温度梯度的响应

我们通过实验室和野外测量确定了辐照度和温度对濒危淡水红藻 Thorea gaudichaudii (Thoreales) 两个异形生活史阶段光合作用的影响。宏观和微观生命史阶段的净氧光合作用-辐照度模型显示出类似的低辐照度适应响应，补偿辐照度 (Ec) 为 6.71 和 2.56 μmol 光子 m-2 s-1（4.30-9.13 和 0.13-7.19， 95% 贝叶斯预测区间，BPI）和饱和辐照度（Ek）分别为 26.6 和 30.0 μmol 光子 m-2 s-1（19.0-37.4 和 12.1-63.0，BPI）。宏观和微观阶段的净光合作用和暗呼吸的温度依赖模型也显示出相似的温度响应，总光合速率 (GPmax) 为 3.54 和 6.34 μg O2 gww−1 min−1 (3. 10–3.99 和 5.31–8.21，BPI），最高时为 32.1 和 35.7°C（29.8–34.0 和 29.5–48.6，BPI）。宏观和微观阶段的最大量子产率 (F v/F m) 对温度的响应也相似；然而，它在低温下有些稳定，在 17.8 和 15.0°C（16.7-18.8 和 12.3-17.1，BPI）时的最大值为 0.54 和 0.62（0.54-0.55 和 0.61-0.63，BPI）。宏观和微观阶段的有效量子产率 (Φ PSII) 也与辐照度呈负相关，辐照度在 12 和 22 处连续暴露于 50（低）和 1000（高）μmol 光子 m-2 s-1 12 小时后降低℃。Φ PSII 的大幅下降和随后的 F v/F m 恢复失败在高辐照度下特别增强，表明光抑制。Φ PSII 的日变化和野外测量宏观阶段的入射辐照度揭示了Φ PSII 的正午低落；然而，由于树木遮荫，几乎没有阳光直射，淡水泉的阴凉处出现了藻类。