Effects of enhanced UV-B radiation on photosynthetic performance and non-photochemical quenching process of intertidal red macroalgae Neoporphyra haitanensis

The effects of enhanced ultraviolet-B (UV-B, 280-320 nm) radiation reaching the Earth's surface has become an important issue in terrestrial and marine ecosystems. Living in the land-marine boundary, intertidal macroalgae have various adaptive strategies to resist drastic environmental changes. In this study, we investigated the effects of enhanced UV-B radiation on the photosynthetic performance and photoprotective mechanisms of the red macroalgae Neoporphyra haitanensis. Our results showed that increasing UV-B radiation inhibited growth, damaged chloroplast structures and photosynthetic pigments, and reduced PSII activity and recovery ability in N. haitanensis. UV-B radiation significantly increased non-photochemical quenching (NPQ), indicating that NPQ is an effective photoprotection strategy in N. haitanensis. The transthylakoid proton gradient (delta pH) uncoupler ammonium chloride (NH4Cl) significantly inhibited NPQ induction, showing that the induction of NPQ in N. haitanensis was dependent on delta pH. Furthermore, violaxanthin and antheraxanthin, essential components of the xanthophyll cycle for modulating NPQ, were not detected in N. haitanensis, indicating the absence of the xanthophyll cycle in N. haitanensis. However, the increased NPQ under UV-B radiation was still associated with the accumulation of zeaxanthin. These findings will be useful for revealing adaptive strategies of intertidal macroalgae to cope with increasing UV-B radiation in the future.

Automated summary

This study investigated the effects of enhanced UV-B radiation on the photosynthetic performance and photoprotective mechanisms of Neoporphyra haitanensis, a red macroalgae. It was found that UV-B radiation inhibited growth, damaged chloroplast structures, and reduced photosynthetic activity in N. haitanensis. Additionally, UV-B radiation increased non-photochemical quenching (NPQ), indicating the activation of effective photoprotection strategies in N. haitanensis. The study also revealed the absence of the xanthophyll cycle, but the accumulation of zeaxanthin under UV-B radiation. These findings are important for understanding the adaptive strategies of intertidal macroalgae to cope with increasing UV-B radiation.