Abstract：
This study investigated the physiological responses of two tropical seagrass species, Halophila ovalis and Thalassia hemprichii, to heat stress under varying light conditions in a controlled 5-day experiment. The experimental design included four treatments: control, saturating light, heat stress under sub-saturating light, and heat stress under saturating light (combined stress). We assessed various parameters, including chlorophyll fluorescence, levels of reactive oxygen species (ROS), antioxidant enzyme activities, and growth rates. In H. ovalis, heat stress resulted in a significant reduction in the maximum quantum yield of photosystem II (Fv/Fm) regardless of the light condition. However, the effects of heat stress on the effective quantum yield of photosystem II (ɸPSII) were more pronounced under saturating light conditions. In T. hemprichii, saturating irradiance exacerbated the heat stress effects on Fv/Fm and ɸPSII, although the overall photoinhibition was less severe than in H. ovalis. Heat stress led to ROS accumulation in H. ovalis and reduced the activity of superoxide dismutase (SOD) and ascorbate peroxidase in the sub-saturating light condition. Conversely, T. hemprichii exhibited elevated SOD activity under saturating light. Heat stress suppressed the growth of both seagrass species, regardless of the light environment. The Biomarker Response Index indicated that H. ovalis displayed severe effects in the heat stress treatment under both light conditions, while T. hemprichii exhibited moderate effects in sub-saturating light and major effects in saturating light conditions. However, the Effect Addition Index revealed an antagonistic interaction between heat stress and high light in both seagrass species. This study underscores the intricate responses of seagrasses, emphasizing the importance of considering both local and global stressors when assessing their vulnerability.
摘要：
这项研究调查了两种热带海草物种的生理反应，卵形嗜盐菌和海氏海螺，在受控的5天实验中，在不同的光照条件下进行热应激。实验设计包括四种治疗方法：对照，饱和光，亚饱和光下的热应力，和饱和光下的热应力（组合应力）。我们评估了各种参数，包括叶绿素荧光，活性氧（ROS）的水平，抗氧化酶活性，和增长率。在H.Ovalis,无论光照条件如何，热应力都导致光系统II的最大量子产率（Fv/Fm）显着降低。然而,在饱和光条件下，热应力对光系统II（PSII）的有效量子产率的影响更为明显。在T.Hemprichii，饱和辐照度加剧了热应激对Fv/Fm和PSII的影响，尽管总体光抑制不如卵圆虫严重。在亚饱和光照条件下，热胁迫导致卵圆虫中ROS的积累，并降低了超氧化物歧化酶（SOD）和抗坏血酸过氧化物酶的活性。相反，红枝在饱和光下表现出升高的SOD活性。热胁迫抑制了两种海草的生长，无论光线环境如何。生物标志物响应指数表明，卵圆石在两种光照条件下的热应激处理中显示出严重的影响。而T.hemprichii在亚饱和光中表现出中等影响，在饱和光条件下表现出主要影响。然而,效应附加指数显示了两种海草物种的热胁迫与强光之间的拮抗相互作用。这项研究强调了海草的复杂反应，强调在评估其脆弱性时同时考虑本地和全球压力源的重要性。
