In near-future climate change scenarios, elevated ocean temperatures with higher and more frequent peaks are anticipated than at present. Moreover, increased eutrophication and higher primary and secondary productivity will affect the oxygen levels of shallow-water coastal ecosystems, creating hypoxic conditions that can be experienced regularly, especially in dense vegetated systems. These climate-related events may impose detrimental effects on the primary productivity of seagrass. To evaluate such effects, this study combined gas exchange measurements with pulse amplitude-modulated fluorometry to assess the impact of short-time exposure to a range of water temperatures at ambient and low-oxygen levels on mitochondrial respiration, chlorophyll fluorescence (based on the F_v/F₀ ratio), photosynthetic oxygen evolution, and photorespiration in leaf segments of the temperate seagrass Zostera marina and the tropical seagrass Thalassia hemprichii. We found that mitochondrial respiration in both Z. marina and T. hemprichii increased with higher temperatures up to 40°C and that low O₂ caused significantly reduced respiration rates, particularly in T. hemprichii. Elevated water temperature had a clear negative effect on the F_v/F₀ of both seagrass species, indicating damage or inactivation of the photosynthetic apparatus, even when light is not present. Moreover, damage to the photosynthetic apparatus was observed as an effect of elevated temperature combined with low O₂ during darkness, resulting in subsequent lower photosynthesis in light. Photorespiration was present, but not promoted by increased temperature alone and will thus not further contribute to productivity losses during warmer events (when not carbon limited). This study demonstrates the negative impact of hypoxic stress and elevated temperatures on seagrass productivity, which may influence the overall health of seagrass plants as well as oxygen and carbon fluxes of shallow-water coastal ecosystems in warmer climate scenarios.

中文翻译：

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不同温度模式下温度和缺氧对海草叶片呼吸，光呼吸和光合作用的影响

在近期气候变化的情况下，预计海洋温度将升高，峰值比现在更高，频率更高。此外，富营养化的提高和初级和次级生产力的提高将影响浅水沿海生态系统的氧气水平，造成低氧条件，可以定期经历，特别是在茂密的植被系统中。这些与气候有关的事件可能会对海草的初级生产力产生不利影响。为了评估这种影响，本研究将气体交换测量结果与脉冲幅度调制荧光分析法相结合，以评估短期暴露于环境温度和低氧水平下一系列水温对线粒体呼吸，叶绿素荧光的影响（基于F _v / F₀比率），光合氧气的释放和温带海草Zostera滨海和热带海草Thalassia hemprichii的叶段中的光呼吸。我们发现，在高达40°C的高温下，滨海假单胞菌和汉普氏酵母的线粒体呼吸都增加，而低O _2会导致呼吸速率显着降低，特别是在汉普氏酵母中。水温升高对F _v / F ₀有明显的负面影响两种海草物种的特征，即使没有光也表明光合作用受到破坏或失活。此外，观察到对光合作用装置的损害，这是由于在黑暗期间升高的温度和较低的O _2的共同作用，导致随后在光下的光合作用降低。存在光呼吸作用，但是光呼吸作用不能单独促进光呼吸作用，因此，在较热的事件中（当碳含量不受限制时）不会进一步造成生产力下降。这项研究证明了低氧胁迫和高温对海草生产力的负面影响，这可能会影响海草植物的整体健康状况，以及在气候变暖的情况下沿海浅水生态系统的氧气和碳通量。