Pupier Chloé A, Bednarz Vanessa N, Grover Renaud, Fine Maoz, Maguer Jean-François, Ferrier-Pagès Christine
Marine Department, Centre Scientifique de Monaco, Monaco, Monaco.
Collège Doctoral, Sorbonne Université, Paris, France.
Front Microbiol. 2019 Aug 14;10:1860. doi: 10.3389/fmicb.2019.01860. eCollection 2019.
Corals are associated with dinitrogen (N)-fixing bacteria that potentially represent an additional nitrogen (N) source for the coral holobiont in oligotrophic reef environments. Nevertheless, the few studies investigating the assimilation of diazotrophically derived nitrogen (DDN) by tropical corals are limited to a single scleractinian species (i.e., ). The present study quantified DDN assimilation rates in four scleractinian and three soft coral species from the shallow waters of the oligotrophic Northern Red Sea using the N tracer technique. All scleractinian species significantly stimulated N fixation in the coral-surrounding seawater (and mucus) and assimilated DDN into their tissue. Interestingly, N fixation was not detected in the tissue and surrounding seawater of soft corals, despite the fact that soft corals were able to take up DDN from a culture of free-living diazotrophs. Soft coral mucus likely represents an unfavorable habitat for the colonization and activity of diazotrophs as it contains a low amount of particulate organic matter, with a relatively high N content, compared to the mucus of scleractinian corals. In addition, it is known to present antimicrobial properties. Overall, this study suggests that DDN assimilation into coral tissues depends on the presence of active diazotrophs in the coral's mucus layer and/or surrounding seawater. Since N is often a limiting nutrient for primary productivity in oligotrophic reef waters, the divergent capacity of scleractinian and soft corals to promote N fixation may have implications for N availability and reef biogeochemistry in scleractinian versus soft coral-dominated reefs.
珊瑚与固氮细菌有关联，在贫营养的珊瑚礁环境中，这些细菌可能是珊瑚共生体额外的氮源。然而，为数不多的关于热带珊瑚对固氮产生的氮（DDN）同化作用的研究仅限于单一的石珊瑚物种（即 ）。本研究采用氮示踪技术，对来自贫营养的红海北部浅水区的四种石珊瑚和三种软珊瑚物种的DDN同化率进行了量化。所有石珊瑚物种都显著刺激了珊瑚周围海水（和黏液）中的固氮作用，并将DDN同化为自身组织。有趣的是，尽管软珊瑚能够从自由生活的固氮菌培养物中吸收DDN，但在软珊瑚的组织和周围海水中未检测到固氮作用。与石珊瑚的黏液相比，软珊瑚的黏液可能是固氮菌定殖和活动的不利栖息地，因为它含有少量的颗粒有机物，氮含量相对较高。此外，已知其具有抗菌特性。总体而言，本研究表明，珊瑚组织对DDN的同化作用取决于珊瑚黏液层和/或周围海水中活性固氮菌的存在。由于氮通常是贫营养珊瑚礁水域初级生产力的限制营养素，石珊瑚和软珊瑚促进固氮的不同能力可能对以石珊瑚为主的珊瑚礁和以软珊瑚为主的珊瑚礁中的氮可用性和礁体生物地球化学产生影响。
