Nitrate respiration and diel migration patterns of diatoms are linked in sediments underneath a microbial mat |
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| Authors: | Elisa Merz Gregory J. Dick Dirk de Beer Sharon Grim Thomas Hübener Sten Littmann Kirk Olsen Dack Stuart Gaute Lavik Hannah K. Marchant Judith M. Klatt |
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| Affiliation: | 1. Max Planck Institute for Marine Microbiology, Celsiusstr. 1, Bremen, Germany;2. Geomicrobiology Lab, Department of Earth & Environmental Sciences, University of Michigan, Ann Arbor, Michigan, USA;3. Department of Botany and Botanical Garden, University of Rostock, Institute of Biosciences, Germany;4. University of Michigan, Cooperative Institute for Great Lakes Research, Ann Arbor, Michigan, USA |
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| Abstract: | Diatoms are among the few eukaryotes known to store nitrate (NO3−) and to use it as an electron acceptor for respiration in the absence of light and O2. Using microscopy and 15N stable isotope incubations, we studied the relationship between dissimilatory nitrate/nitrite reduction to ammonium (DNRA) and diel vertical migration of diatoms in phototrophic microbial mats and the underlying sediment of a sinkhole in Lake Huron (USA). We found that the diatoms rapidly accumulated NO3− at the mat-water interface in the afternoon and 40% of the population migrated deep into the sediment, where they were exposed to dark and anoxic conditions for ~75% of the day. The vertical distribution of DNRA rates and diatom abundance maxima coincided, suggesting that DNRA was the main energy generating metabolism of the diatom population. We conclude that the illuminated redox-dynamic ecosystem selects for migratory diatoms that can store nitrate for respiration in the absence of light. A major implication of this study is that the dominance of DNRA over denitrification is not explained by kinetics or thermodynamics. Rather, the dynamic conditions select for migratory diatoms that perform DNRA and can outcompete sessile denitrifiers. |
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