The effect of nitrogen limitation on cellular DMSP and DMS release in marine phytoplankton: climate feedback implications
Résumé
The effect of nitrogen limitation on intracellular dimethylsulfoniopropionate (DMSP) and its enzymatic cleavage to dimethylsulfide (DMS) was investigated in semi-continuous cultures of the coccolithophore Emiliania huxleyi and the chain-forming coastal diatom Skeletonema costatum, both ecologically important species. The diatom had a DMSP/C molar ratio of 0.0020 (1% of cell carbon) under nutrient sufficient conditions, and increased its DMSP/C ratio by 70% under nitrogen limitation. The coccolithophore had a constitutively high intracellular DMSP concentration (~200 mmol per liter of cell volume, an estimated 5% of cell carbon) and Nlimitation of this species caused no measurable increase inDMSP. Instead, N-limitation of this species increased the activity of the DMSP cleavage enzyme, DMSPlyase, which resulted in a 20-fold increase in the moles of DMS in the culture per unit of cell volume and a 40- to 80-fold increase in the ratio of DMS to chl a. Our results and previously published findings suggest that N-limitation is likely a contributing factor to the extremely high DMS:chl a ratios observed in nutrient limited surface ocean waters under thermally stratified conditions. Thus, N-limitation may play a role in climate feedback mechanisms involving biologically derived DMS.