Nitrogen pollution and pesticides such as photosystem II (PSII) inhibitor herbicides have several detrimental impacts on coral reefs, including breakdown of the symbiosis between host corals and photosynthetic symbionts. Although nitrogen and PSII herbicide pollution separately cause coral bleaching, the combined effects of these stressors at environmentally relevant concentrations on corals have not been assessed. Here, we report the combined effects of nitrate enrichment and PSII herbicide (prometryn) exposure on photosynthesis, oxidative status and endosymbiont community diversity of the reef-building coral Acropora hyacinthus. Coral fragments were exposed in a mesocosm system to nitrate enrichment (9 μmol/L) and two prometryn concentrations (1 and 5 μg/L). The results showed that sustained prometryn exposure in combination with nitrate enrichment stress had significant detrimental impacts on photosynthetic apparatus [the maximum quantum efficiency of photosystem II (Fv/Fm), nonphotochemical quenching (NPQ) and oxidative status in the short term. Nevertheless, the adaptive mechanism of corals allowed the normal physiological state to be recovered following 1 μg/L prometryn and 9 μmol/L nitrate enrichment individual exposure. Moreover, exposure for 9 days was insufficient to trigger a shift in Symbiodiniaceae community. Most importantly, the negative impact of exposure to the combined environmental concentrations of 1 μg/L prometryn and 9 μmol/L nitrate enrichment was found to be significantly greater on the Fv/Fm, quantum yield of non-regulated energy dissipation [Y(NO)], NPQ, and oxidative status of corals compared to the impact of individual stressors. Our results show that interactions between prometryn stress and nitrate enrichment have a synergistic impact on the photosynthetic and oxidative stress responses of corals. This study provides valuable insights into combined effects of nitrate enrichment and PSII herbicides pollution for coral's physiology. Environmental concentrations of PSII herbicides may be more harmful to photosystems and antioxidant systems of corals under nitrate enrichment stress. Thus, future research and management of seawater quality stressors should consider combined impacts on corals rather than just the impacts of individual stressors alone.

氮污染和光系统 II (PSII) 抑制剂除草剂等杀虫剂对珊瑚礁产生多种不利影响，包括破坏宿主珊瑚和光合共生体之间的共生关系。尽管氮和 PSII 除草剂污染分别导致珊瑚白化，但这些压力源在环境相关浓度下对珊瑚的综合影响尚未得到评估。在这里，我们报告了硝酸盐富集和 PSII 除草剂（扑草净）暴露对造礁珊瑚 Acropora hyacinthus 的光合作用、氧化状态和内共生群落多样性的综合影响。珊瑚碎片在中生态系统中暴露于硝酸盐富集（9 μmol/L）和两种浓度的扑草净（1 和 5 μg/L）。结果表明，持续的扑草净暴露与硝酸盐富集胁迫相结合，对光合装置[光系统II的最大量子效率（Fv/Fm）、非光化学猝灭（NPQ）和短期氧化状态产生显着的有害影响。然而，珊瑚的适应机制允许在1μg/L扑草净和9μmol/L硝酸盐单独暴露后恢复正常的生理状态。此外，暴露9天不足以引发共生科群落的转变。最重要的是，暴露于 1 μg/L 扑草净和 9 μmol/L 硝酸盐浓缩物的组合环境浓度中的负面影响被发现对 Fv/Fm、非调节能量耗散的量子产率显着更大 [Y(NO )]、NPQ 和珊瑚的氧化状态与个体压力源的影响相比。我们的结果表明扑草净应激和硝酸盐富集之间的相互作用对珊瑚的光合作用和氧化应激反应具有协同影响。这项研究为了解硝酸盐富集和 PSII 除草剂污染对珊瑚生理的综合影响提供了宝贵的见解。PSII 除草剂的环境浓度可能对处于硝酸盐富集胁迫下的珊瑚的光系统和抗氧化系统造成更大的危害。因此，未来海水质量压力源的研究和管理应考虑对珊瑚的综合影响，而不仅仅是单个压力源的影响。