Effects Of Different Nutrient Conditions On The Production Of Dimethysulfide (DMS) And Dimethylsulfoniopropionate (DMSP) By Four Marine Algae

The climaticlly relevant trace gas dimethysulfide （DMS） is one dominant volatile organicbiogenic compound in the surface ocean. The algal osmolyte dimethylsulfoniopropionate（DMSP）, synthesized by phytoplankton as an internal cell component, is the major precursor ofmarine DMS. In this thesis, the production of DMS and DMSP by marine microalgae wasinvestigated to elucidate the role of marine phytoplankton in ocean-atmosphrer interactions inthe global biogeochemical sulfur cycle.1. The production of DMS and DMSP by four species of unicellular algaeThe production of dimethylsulfide （DMS） and dimethylsulfoniopropionate （DMSP） in thecultures of four algae including Phaeocystis globosa, Pseudo-nitzschia pungens, Nitzschiaclosterium and Alexandrium tamarense, was studied in different growth stages. Moveover, thebasic physiology of DMS and DMSP in axenic cultures was studied with a focus on the effectsof varying levels of N/P ratios （0:1,5:1,20:1,50:1）, and varying concentrations ofphosphorous and iron （10,100,1000nmol·L-1） on the cell density and DMS/DMSP contentsbacause these factors have been demonstrated to be important controls on DMS and DMSPdynamics in the marine enviroment. The main research results were summarized as follows:（1） The concentration of DMS had a lag of1-2d relative to DMSPd, the production rate ofDMSPd in the culture of Phaeocystis globosa was2-3fold higher than that in the culturesof other three microalgae, and the production rate of DMSPp by Phaeocystis globosa was6-7times higher than that by other three marine algae. A close correlation was foundbetween the DMSPp and chlorophyll a concentrations. The production of DMSPp per unitcell mass was the highest in the culture of Alexandrium tamarense. In the experimentalperiod, the DMS concentration varied basically following variation in the DMSPdconcentration. In the cultures, the concentrations of DMS were in the following sequence:Phaeocystis globosa≈Alexandrium tamarense> Pseudo-nitzschia pungens≈Nitzschiaclosterium. However, for the production of DMS by unit cell mass, Alexandrium tamarensewas maximum and Phaeocystis globosa was minimum.（2） The limitation of nitrogen and phosphorus had a great impact on the growth of Phaeocystisglobosa, and the optimum growth of Phaeocystis globosa was found under thephosphorus-replete condition with N/P=50:1. The Pseudo-nitzschia pungens had the highercell density incubated under the phosphorus-replete condition with N/P=5:1orphosphorus-depleted condition with N/P=50:1. Nitzschia closterium culture had lower celldensity under phosphorus-deplete condition, because the growth of this alga was highlydependent upon the level of phosphorus. Alexandrium tamarense could enter theexponential growth phase earliest in phosphorus-replete condition with N/P=50:1andexhibited the maximum cell density.（3） No significantly difference appeared in the DMSPd concentrations in different control groups in the cultures of Phaeocystis globosa. In contrast, the DMSPp concentrations in thecultures of Phaeocystis globosa were higher under the phosphorus-replete condition than inthe phosphorus-depleted condition. The nutrition of nitrogen and phosphorus did notbecome limiting factor to the DMSP production by Pseudo-nitzschia pungens. The DMSPpproduction by Nitzschia closterium was generally higher in phosphorus-depleted conditionwith N/P=50:1. The DMS level in the culture of Alexandrium tamarense with higher N/Pratio was2.5-fold higher than that with lower N/P ratio.（4） High Fe³⁺concentration could stimulate the growths of Pseudo-nitzschia pungens,Nitzschia closterium and Alexandrium tamarense, but inhibited the growth of Phaeocystisglobosa. The DMSPd contents in the culture of Pseudo-nitzschia pungens increased withincreasing Fe³⁺concentration, but the DMSPd production by Phaeocystis globosadecreased with the increase of Fe³⁺concentration. High Fe³⁺concentration enhancedobviously the DMS production by Pseudo-nitzschia pungens, but decreased the DMSproduction by Alexandrium tamarense.2. The ship-based mesocosm experiment in the Yellow SeaVariations in the concentration of DMSP, DMS and DMSO and the factors influencingthem were investigated in the ship-based mesocosm experiments conducted in the Yellow Seain October2011. The main research results were obtained as follows. For all the experimentalgroups, the cell density of phytoplankton reached maxima at day10or11. Nitrogen limitationplayed a blocking effect on the phytoplankton growth in the mesocosm. In the mesocosm ofM4(with Fe³⁺added), the DMSPd concentration rapidly reached maximum and then decreasedat high-speed, but no significant variation appeared in the DMSPd concentration in the otherincubation groups. In addition, no consitent trend was found for DMSPp concentrations in fiveincubation groups except M6（control group）. It is noteworthy that the limination of nutritioncould enhance the DMS production. The N/P ratio consistent with the ratio of Redfield and theaddition of iron were favorable to the production of DMSOd. In the mesocosm experiments,DMSOp exhibited a consistent change trend with chlorophyll a and therefore a significantrelationship appeared between the DMSOp and chlorophyll a concentrations.