Coupling of dimethylsulfoniopropionate production and carbon fixation in four temperate phytoplankton species excludes active short-term regulation of dimethylsulfoniopropionate synthesis under increased light-stress

The production of the secondary metabolite dimethylsulfoniopropionate (DMSP) by marine microalgae has a strong impact on the global sulfur cycle, as DMSP is the precursor of the climate active gas dimethylsulfide. Quantifying the impact of abiotic parameters on DMSP production is needed to accurately depict DMSP production in ecosystem models. In this study, we investigated if de novo production of DMSP was upregulated under short-term elevated irradiance and ultraviolet A radiation (UVA-R). We exposed high-light and low-light acclimated cultures of Emiliania huxleyi, Tetraselmis sp., Thalassiosira oceanica, and Phaeodactylum tricornutum to high irradiance and UVA-R treatments and followed de novo DMSP production and carbon fixation. We show that combined photosynthetically active radiation and UVA-R resulted in increased net photoinhibition rates, but decreased specific DMSP production and growth compared to non-UVA-R treatments for all species. Photoacclimation to high photosynthetically active radiation resulted in a decreased UVA-R sensitivity and positively affected the DMSP-to-carbon concentration ratios within the cultures. We conclude that there is no active short-term upregulation of DMSP production under elevated photosynthetically active radiation and UVA-R. Instead, the production of DMSP in response to light-stress is closely coupled to particulate organic carbon production in all cases. While the relatively high cellular concentrations of DMSP do not exclude a de facto antioxidant function, its production is likely regulated by other cellular processes, for example, an overflow mechanism. The data of this study aim to improve the mechanistic understanding of DMSP synthesis, as well as to quantify DMSP production rates in different marine phytoplankton species.