Archaea regulate the biogeochemical processes of ocean systems.The Changjiang(Yangtze)River estuary(CRE) is a complex and dynamic area strongly affected by seawaters and ocean currents.In this study,the planktonic archaeal communities in the surface and bottom seawaters of the CRE were investigated.Significant differences in the archaeal community composition were found between the surface and bottom seawaters(P<0.001).Marine Group Ⅱ(MG-Ⅱ) was dominant in the surface layers,and Nitrosopumilales was enriched in the bottom layers.Marine Group Ⅲ(MG-Ⅲ) was more abundant in the bottom layers than in the surface ones(P<0.001).These results were completely different from previous findings in the CRE seawater.Instead of dissolved oxygen(DO),temperature and salinity were the most vital environmental variations in the distribution of the archacal communities.According to the predicted metabolic pathways,the following functional subcategories were enriched in the hypoxic condition:replication and repair,membrane transport,glycan biosynthesis and metabolism,amino acid metabolism,metabolism of cofactors and vitamins,and xenobiotics biodegradation and metabolism(P<0.001),which indicated the strong adaptability of archaea to the harsh environment in the bottom seawater.These findings expand the understanding on archaeal structure and functions in the surface and bottom seawaters,including the hypoxic zones in the CRE,and may contribute to further works of the archaeal community in the CRE.
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