Pressure-induced leakage of dissolved organic matter (DOM) from different diatom species

Four diatom strains obtained from different culture collections were grown to stationary phase in L1 medium plus silicate (Guillard & Hargraves 1993) at 15°C under a light/dark regime of 14/10 h. For experimentation, the diatom strains were incubated at either atmospheric pressure (0.1 MPa = control treatment) or at gradually increasing hydrostatic pressure (0.1-100 MPa = pressure treatment) throughout 21 days in darkness and at 3°C. The pressure treatment simulated the sinking of particle-associated diatoms from the ocean surface down into a hadal trench of 10 km depth. Pressure-induced leakage of dissolved organic matter (DOM) was followed throughout the incubations. Both ambient concentrations and intracellular concentrations of different DOM components were measured: Dissolved organic carbon (DOC), total dissolved nitrogen (TDN), protein-like and humic-like DOM fluorescence, total proteins, total polysaccharides, laminarin, and dimethylsulfoniopropionate (DMSP). The cell abundance of the different diatom strains was followed throughout the incubations.