A better understanding of species and population responses to thermal stress is critical to predict changes in their distribution under warming scenarios. Seagrasses are a unique group of marine plants that play fundamental roles in marine environments and provide vital ecosystem services. Nevertheless, previous studies on seagrass thermal tolerance have focused exclusively on a handful of species, with the majority of these remaining virtually unexplored. Moreover, to date, no study has compared the response to thermal stress between northern and southern hemisphere seagrasses. Here, we conducted comparative mesocosm experiments using four seagrass species from the northern (i.e. Mediterranean: Posidonia oceanica, Cymodocea nodosa) and southern (i.e. Australia: Posidonia australis and Zostera muelleri) hemisphere as representative of two different life strategies, i.e. climax (P. oceanica, P. australis) and pioneer (C. nodosa, Z. muelleri). Plants acclimatized to the mesocosm conditions at ambient temperature (i.e. 26 °C) during a 5-week period, were exposed to a simulated marine heatwave (i.e. 32 °C) for 2 weeks. Measurements of plant responses, including photo-physiology, morphology, and pigment content, were performed at the end of the warming exposure. Results showed that warming had no significant effects on photosynthetic performances of northern hemisphere seagrasses while negatively impacted their southern hemisphere counterparts. Similarly, warming favored the growth of northern hemisphere plants, but strongly inhibited the development of southern hemisphere species. Furthermore, photo-physiological and pigment content results suggested pioneer seagrasses better dealt with warming than climax species. Our study provides more insights into the field of seagrass ecology and yields potential implication for future seagrass conservation and restoration activities.

更好地了解物种和种群对热应激的反应对于预测其在变暖情景下的分布变化至关重要。海草是一组独特的海洋植物，在海洋环境中发挥着重要作用，并提供重要的生态系统服务。尽管如此，之前关于海草耐热性的研究只集中在少数物种上，其中大部分几乎未被探索。此外，迄今为止，还没有研究比较北半球和南半球海草对热应力的反应。在这里，我们使用来自北部（即地中海：Posidonia Oceanica、Cymodocea nodosa）和南部（即澳大利亚：Posidonia australis和Zostera muelleri ) 半球代表两种不同的生活策略，即高潮 ( P. Oceanica , P. australis ) 和先锋 ( C. nodosa , Z. muelleri)）。在 5 周期间适应环境温度（即 26°C）下的中宇宙条件的植物暴露于模拟海洋热浪（即 32°C）下 2 周。在变暖暴露结束时进行植物反应的测量，包括光生理学、形态学和色素含量。结果表明，变暖对北半球海草的光合性能没有显着影响，而对其南半球海草的光合性能产生负面影响。同样，变暖有利于北半球植物的生长，但强烈抑制了南半球物种的发育。此外，光生理和色素含量结果表明，先驱海草比高潮物种更好地应对变暖。