Data from: A three-stage symbiosis forms the foundation of seagrass ecosystems

Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve–sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.

海草（seagrass）约于1亿年前从陆生植物演化而来，成为海洋基础物种（marine foundation species）。然而其生态成功的机制至今仍是未解之谜——因为海草床内天然有机质的积累本应导致沉积物中硫化物浓度达到有毒水平。本研究通过荟萃分析（meta-analysis）、野外实地研究与实验室控制实验，揭示了海草、满月蛤类双壳动物与其鳃部硫化物氧化共生菌之间古老的三阶段共生体系如何缓解海草所面临的硫化物胁迫。研究发现，双壳动物与硫化物氧化菌的共生体系可降低沉积物硫化物浓度，并通过生物量指标提升海草的生长量。反过来，海草根系的径向泌氧过程与海草床内的有机质积累，为双壳动物及其内共生体提供了生存益处。上述研究结果阐明了海草在温暖水域长期存续的机制，同时为海草生态系统的保护提供了全新的研究方向与应用前景。