Dimethylsulphoniopropionate (DMSP) production of Gephyrocapsa oceanica in response to environmental forcing

2017-02-14T00:23:29Z (GMT) by Larsen, Stuart Henry
Dimethyl sulphide (DMS) is an important trace gas, both for its contribution to the global sulphur cycle and also, when oxidised in the atmosphere to sulphates, for its potential to alter the properties of clouds and so potentially affect climate. The precursor to DMS, dimethylsulphoniopropionate (DMSP), is produced by a number of marine micro-algae. This study investigated the role of temperature (10-30C), salinity (20-45), photosynthetically active radiation (PAR, 0-2000+ micromol photons m-2 s-1), daylength, rapidly varying light intensity, CO2 concentration and ambient PAR, ultraviolet A and B exposures on the physiology and production of DMSP in the coccolithophore Gephyrocapsa oceanica. Increasing temperature or CO2 concentration led to decreased cellular DMSP and net DMSP production. Increased PAR, up to the point of photoinhibition (which for G. oceanica} is about 1200 micromol photons m-2 s-1), daylength, salinity and potentially UVR were associated with increased cellular DMSP. Increased PAR above that causing photoinhibition resulted in decreased cellular and net DMSP production. The rate of photosynthetic carbon fixation was modelled as a function of incident light, temperature and CO2 concentration. While the photochemistry of photosystems I and II is essentially temperature independent, the process of carbon assimilation is not. The cell must continually match the photochemical production of reactive oxygen species (ROS) and reductant with the ability of the Calvin-Benson cycle to utilise this reductant to fix carbon, as this is not possible, an antioxidant system is also required. Low temperatures, and/or low CO2 concentrations, both of which reduce the carbon fixation rate, and/or increased PAR, UVR and/or salinity all potentially lead to an increased need for an antioxidant system to be up-regulated and vice versa. Both the experimental and modelling results obtained are consistent with the hypothesis that DMSP acts as such an antioxidant within the cell, and for salinity, that it may act both as an antioxidant and a compatible osmolyte.