While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO₂ levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO₂ concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O₂-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (F_k) of Kautsky curves relative to the amplitude of F_J−F_o (W_k) and a decrease of the maximum quantum yield of PSII (F_v/F_m). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO₂ assimilation. When the algal thalli were grown under increased CO₂ and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO₂ levels and OA.

虽然潮间带大型藻类在日光循环期间暴露于太阳光合有效辐射 (PAR) 和紫外线辐射 (UVR) 的剧烈变化，以及与 CO ₂水平增加相关的海洋酸化 (OA) ，但对它们在大气条件下的光合性能知之甚少。这些驱动因素的综合影响。在这项工作中，我们研究了控制电子流通过光系统 II (PSII) 和光系统 I (PSI) 的光保护策略，以响应有或没有 UVR 的太阳辐射以及潮间带商业上重要的红色巨藻中CO ₂浓度升高焦化 （之前 紫菜) 条藻. 通过使用叶绿素荧光技术，我们发现单独高水平的 PAR 会诱导光系统间电子传输载体的光抑制，这可以通过考茨基曲线的 J 和 I 步中叶绿素荧光的增加来证明。在存在 UVR 的情况下，光诱导的抑制主要在 O ₂进化复合物 (OEC) 和 PSII 中发现，这可以通过 K 步的可变荧光显着增加来证明。F_k ) 的考茨基曲线相对于F_J -F_o (W _k ) 和 PSII 的最大量子产率的降低 (F_v /F_米）。这种抑制似乎改善了下游电子受体的功能，防止 PSI 过度还原。反过来，稳定的 PSI 活性提高了 PSI 周围的循环电子传递 (CET) 效率，消散了多余的能量并为 CO ₂同化提供了 ATP 。当藻菌体在增加的CO ₂和OA 条件下生长时，CET 活性进一步增强，从而保持OEC 稳定性，从而显着减轻UVR 诱导的光抑制。总之，PSII 和 PSI 之间完善的协调赋予了条斑紫菜具有响应 UVR 的高效光化学性能，尤其是在未来 CO ₂水平和 OA增加的情况下。