Growth, DMS and DMSP production in Emiliania huxleyi under elevated CO₂ and UV radiation

The effects of ocean acidification and solar radiation on marine organisms have received increasing attention. Coccolithophores are a major producer of dimethylsulfoniopropionate (DMSP), which is a precursor of dimethylsulfide (DMS), a volatile biogenic active gas related to climate. Here, we investigated the individual and combined effects of elevated CO₂ and ultraviolet radiation (UVR) on growth, DMS, and DMSP production of Emiliania huxleyi. Elevated CO₂ (1000 μatm, HC) decreased the cell concentration, DMS, and particulate DMSP (DMSP_p) concentrations by 17%, 20%, and 13%, respectively, compared with ambient CO₂ (400 μatm, LC) in the semi-continuous culture. The addition of UVA to photosynthetically active radiation (PAR) increased cell concentration of E. huxleyi by 16% on day 4, which may be due to the photorepair effects induced by UVA, and the effect was time-dependent. PAR + UVA and PAR + UVA + UVB exposure decreased cellular DMS by 25%-56%, and increased cellular DMSP_p by 60%-130% compared with PAR on days 3-4. Cellular DMSP_p followed the order: PAR + UVA > PAR + UVA + UVB > PAR, and HC had no significant effects on cellular DMSP_p compared with LC in the combined experiment. These results aid our understanding of the effects of ocean acidification and UV radiation on the production of methyl sulfur compounds in the ocean.