Nitrate respiration and diel migration patterns of diatoms are linked in sediments underneath a microbial mat.

Diatoms are among the few eukaryotes known to store nitrate (NO ) and to use it as an electron acceptor for respiration in the absence of light and O . Using microscopy and N 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 NO 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.