Hadal trench sediments are hotspots of biogeochemical activity in the deep sea, but the biogeochemical and ecological factors that shape benthic hadal microbial communities remain unknown. Here, we sampled ten hadal sites from two trench regions with a vertical resolution of down to 1 cm. We sequenced 16S rRNA gene amplicons using universal and archaea-specific primer sets and compared the results to biogeochemical parameters. Despite bathymetric and depositional heterogeneity we found a high similarity of microbial communities within each of the two trench axes, while composition at the phylum level varied strongly with sediment depth in conjunction with the redox stratification into oxic, nitrogenous, and ferruginous zones. As a result, communities of a given sediment horizon were more similar to each other across a distance of hundreds of kilometers within each trench, than to those of adjacent horizons from the same sites separated only by centimeters. Total organic carbon content statistically only explained a small part of the variation within and between trenches, and did not explain the community differences observed between the hadal and adjacent shallower sites. Anaerobic taxa increased in abundance at the top of the ferruginous zone, seeded by organisms deposited at the sediment surface and surviving burial through the upper redox zones. While an influence of other potential factors such as geographic isolation, hydrostatic pressure, and non-steady state depositional regimes could not be discerned, redox stratification and diagenesis appear to be the main selective forces that structure community composition in hadal sediments.
Bibliografisk noteFunding Information:
Advanced grant “Benthic diagenesis and microbiology of hadal trenches” #669947 and the Danish National Research Foundation grant DNRF145 to establish the Danish Center for Hadal Research, both awarded to Ronnie N. Glud. This work is part of the “Pourquoi Pas les Abysses?” project funded by Ifremer, and the project eDNAbyss (AP2016 -228) funded by France Génomique (ANR-10-INBS-09) and Genoscope-CEA. Lastly, we would like to acknowledge that the suggestions from the reviewers greatly improved this manuscript.
Acknowledgements We would like to thank Per Martensen (SDU, Denmark), Mathias Zabel (Marum, Germany), Morten Larsen (SDU, Denmark), and Anni Glud (SDU, Denmark) for technical assistance and fruitful scientific discussions. Furthermore, our gratitude goes to the captains, crews, and scientific personnel of the RV Sonne (SO261; ship time provided by BMBF, Germany, awarded to Frank Wenz-hoefer, Mathias Zabel, and Ronnie N. Glud) and RV Tangaroa (TAN1711; shiptime partly funded by Coasts & Oceans Centre of New Zealand’s National Institute of Water & Atmospheric Research (NIWA), awarded to Ashley A. Rowden and Ronnie N. Glud). Financial support for the study was provided by HADES-ERC
© 2021, The Author(s).