Department of Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, 02543, USA.
ISME J. 2021 Apr;15(4):1222-1235. doi: 10.1038/s41396-020-00845-2. Epub 2020 Dec 20.
Coral reef health depends on an intricate relationship among the coral animal, photosynthetic algae, and a complex microbial community. The holobiont can impact the nutrient balance of their hosts amid an otherwise oligotrophic environment, including by cycling physiologically important nitrogen compounds. Here we use N-tracer experiments to produce the first simultaneous measurements of ammonium oxidation, nitrate reduction, and nitrous oxide (NO) production among five iconic species of reef-building corals (Acropora palmata, Diploria labyrinthiformis, Orbicella faveolata, Porites astreoides, and Porites porites) in the highly protected Jardines de la Reina reefs of Cuba. Nitrate reduction is present in most species, but ammonium oxidation is low potentially due to photoinhibition and assimilatory competition. Coral-associated rates of NO production indicate a widespread potential for denitrification, especially among D. labyrinthiformis, at rates of ~1 nmol cm d. In contrast, A. palmata displays minimal active nitrogen metabolism. Enhanced rates of nitrate reduction and NO production are observed coincident with dark net respiration periods. Genomes of bacterial cultures isolated from multiple coral species confirm that microorganisms with the ability to respire nitrate anaerobically to either dinitrogen gas or ammonium exist within the holobiont. This confirmation of anaerobic nitrogen metabolisms by coral-associated microorganisms sheds new light on coral and reef productivity.
珊瑚礁的健康取决于珊瑚动物、光合藻类和复杂微生物群落之间的复杂关系。在原本贫营养的环境中，后生动物可以通过循环生理上重要的氮化合物来影响宿主的养分平衡。在这里，我们使用 N 示踪实验首次对古巴杰尔达斯德拉雷纳保护区内五种标志性造礁珊瑚（Acropora palmata、Diploria labyrinthiformis、Orbicella faveolata、Porites astreoides 和 Porites porites）的氨氧化、硝酸盐还原和氧化亚氮（NO）生成进行了同步测量。大多数物种都存在硝酸盐还原，但由于光抑制和同化竞争，氨氧化水平较低。珊瑚相关的 NO 生成速率表明存在广泛的反硝化潜力，特别是在 D. labyrinthiformis 中，速率约为 1 nmol cm d。相比之下，A. palmata 显示出最小的主动氮代谢。增强的硝酸盐还原和 NO 生成速率与暗网呼吸期同时观察到。从多种珊瑚物种分离的细菌培养物的基因组证实，后生动物内存在能够将硝酸盐厌氧呼吸为氮气或铵盐的微生物。这一发现证实了珊瑚相关微生物的厌氧氮代谢，为珊瑚和珊瑚礁的生产力提供了新的认识。
