Stuides On Biological Production And Consumption Of DMS And DMSP In Seawater

In marine waters, the most abundant volatile biogenic sulfur compound dimethylsulfide (DMS) is considered to play significant roles in the natural sulphur cycle and has a potential influence on Earth's climate change and the environmental acidification due to its oxidation products in the atmosphere. Dimethylsulfoniopropionate (DMSP) is the major precursor of DMS and DMSP can be degraded to DMS and acrylic acid by DMSP cleavage lyase. The biological production and consumption of DMS are considered to be the principal mechanisms controlling the concentration of DMS in the surface ocean and its sea-to-air flux, and play a key role in the global biogeochemical cycle of DMS and DMSP. Therefore studies on the biological production and consumption of DMS and its precursor DMSP in the surface ocean offer a unique opportunity to make the assessment of the quantitative contributions of halobios to DMS and DMSP accumulations in the ocean, which will be helpful to understand better the biogeochemistry processes of DMS and DMSP.In the present dissertation, at first, we choose the North Yellow Sea as the study area that is affected seriously by human activities. The spatial and temporal variations of DMS biological production and consumption rates and the factors influencing them are systematically studied. The relatively importance of biological consumption and sea-to-air emission for the DMS removal process in the surface water is evaluated. Secondly, we focus on the production of DMS and DMSP during the growth stages of three typical offshore algae by laboratory culture experiment. Other objectives of this study are to assess the bio-availablility of DMSPd and to examine quantitatively the contributions of DMSP consumption to DMS production in coastal water of the Gulf of Mexico. The main conclusions are drawn as follows:1. Studies on the biological production and consumption rates of DMS in the North Yellow Sea and the factors influencing them(1) The biological production and consumption rates of DMS are determined in the North Yellow Sea during December,2006-January,2007, April-May,2007 and October,2007. In the surface water, the biological production and consumption rates of DMS in winter are 5.41 (1.91～13.0) and 3.84 (0.81～11.6) nM d-1, respectively. In spring, the corresponding rates are 6.24 (2.38～18.9) and 3.71 (1.74～13.2) nM d-1, respectively. During autumn, DMS production and consumption rates are 7.35 (2.04～15.9) and 5.67 (1.67～13.8) nM d-1, respectively. Our results demonstrate that, for DMS biological production rate, highest and lowest values occur in autumn and in winter, respectively; the peak of DMS consumption rate appear in autumn compared to the corresponding values in winter and spring. On average, the DMS production and consumption rates during these three seasons are 6.39±0.152 and 4.41±0.249 nM d-1, respectively. Moreover, both DMS biological production and consumption rates display a similar spatial pattern in different seasons. In winter, the peaks of DMS production and consumption rates coincidently appear near the Liaodong and Shandong Peninsula and the lower values occur in the center of the North Yellow Sea. In spring, the minimum and maximum of DMS production/consumption rates are found in the estuary of Yalu River and in the southeast of Liaodong Peninsula, respectivley. During autumn, the higher and lower values of DMS production/consumption rates appear at inshore locations lying in the south of Liaodong Peninsula and at offshore sites in the center of North Yellow Sea, respectively.(2) The biological production and consumption of DMS are influenced by various biological and environmental factors such as in situ temperature, salinity, DMS and DMSPd concentrations, Chl a level and the composition of phytoplankton species. In winter, Chl a concentration as well as seawater surface temperature and DMSPp concentration plays a significant role in DMS biological production. During spring and autumn, DMS biological production rates are influenced obviously by the DMSPd and DMSPp concentrations. In winter and autumn, in situ DMS concentration is the important factor for the DMS consumption rate; moreover, seawater surface temperatue and salinity are responsible for DMS consumption in winter. In the surface water of North Yellow Sea, physical, chemical and biological factors definitely influence DMS production and consumption, but the degree of influence is the issue during spring, autumn and winter.(3) In general, DMS biological production is of a magnitude similar to DMS biological consumption and the DMS production exceeded its cleavage by an average factor of 65%. This discrepancy is bound to result in the net DMS biological production which might be balanced by other DMS removal processes. A strong positive correlation present between DMS production and consumption, indicating the intimate interrelation between the DMS biological formation and its microbial cleavage. During winter, spring and autumn, the biological turnover times of DMS in the subsurface water are 0.834 (0.2～1.73),1.59 (0.406～4.65) and 0.666 (0.240～1.36) d, respectively; the sea-to-air turnover times of DMS are 6.30 (0.122～32.3),5.04 (0.868～32.6) and 10.0 (0.635～56.2) d, respectively. On average, the rate ratios of DMS bio-consumption to sea-to-air turnover rates are 10.95,3.97,17.94, respectively, in winter, spring and autumn. Thus the above observations lead to a clear conclusion that the crucial sink of DMS in the surface water is bacterial consumption, which greatly exceeds its sea-to-air emission in the upper water column for our study area.2. Studies on DMS and DMSP produced by three species of marine algaeThe production of DMS and DMSP are studied in different growth stages of Phaeodactylum tricornutum, Prorocentrum micans, Isochrysis galbana 8701. Moreover, we have studied the basic physiology of DMSP and DMS in axenic cultures, focusing on effects of varying levels of salinity, NO3-, Fe3+ and SiO32- on cell abundances, DMS and DMSP contents of these three algae as these factors have been found to be important controls on DMSP and DMS dynamics in the seawater. The results are shown as follows:(1) On the whole, the DMSPd and DMSPp concentrations per Chl a of Prorocentrum micans cultures are higher than those of Phaeodactylum tricornutum and Isochrysis galbana 8701. DMS has low concentration in the exponential growth stage and stationary growth stage; in the senescent stage, the algae cells produce the largest amount of DMS.(2) High nitrate level has an inhibition function on DMSPp production of Phaeodactylum tricornutum and Prorocentrum micans; the effects of nitrate concentration on the DMSPp production of Isochrysis galbana 8701 are not significant. In Prorocentrum micans cultures with the lowest nitrate level, the DMSP/Chl a values are 7-fold higher than those in cultures with highest nitrate level.(3) The promotion function of DMS and DMSP production by Phaeodactylum tricornutum and Prorocentrum micans are caused by high salinity, vice versa. DMSP content and DMS production are not markedly different in the Isochrysis galbana 8701 cultures amended with different salinities.(4) High Fe3+ concentration stimulates DMSPd production of Phaeodactylum tricornutum and Prorocentrum micans, but inhibits that of Isochrysis galbana 8701. The intracellular DMSP contents of Isochrysis galbana 8701 increase with increasing Fe3+ concentration, but intracellular DMSP production of Prorocentrum micans decreases with Fe3+ concentration increase. High Fe3+ concentration enhances obviously the DMS production by Prorocentrum micans and Isochrysis galbana 8701, but the effects of Fe3+ concentration on the DMS and DMSPp production of Phaeodactylum tricornutum are not significant.(5) Compared to medium and highest SiO32- concentrations, lowest SiO32-concentration is helpful to intracellular DMSP accumulation and DMS production of Phaeodactylum tricornutum.3. Assessment of the bio-availability and turnover of dissolved Dimethylsulfoniopropionate (DMSP) in coastal waters of the Gulf of MexicoDissolved dimethylsulfoniopropionate (DMSPd) is an important substrate for marine bacteria and a precursor of reactive sulfur gases. We compared biological consumption rates of DMSPd in coastal seawater determined by two different methods, an inhibitor approach with the established DMSP-uptake inhibitor glycine betaine (GBT), and the 35S-DMSP tracer loss kinetics approach. Both approaches rely on determination of the DMSPd concentration, which was measured by small volume drip filtration (SVDF) through Whatman GF/F filters (0.7μm nominal retention) and subsequent base hydrolysis of the DMSP to DMS. In unfiltered coastal seawater, the 35S-DMSP tracer method yielded DMSPd turnover fluxes of (35.7～215 nM d-1) that were 1.7 to 152 times higher than those obtained in parallel samples with the inhibitor method (0.34～21.6 nM d-1). Further tests confirmed that GBT strongly inhibited DMSPd degradation and that 35S-DMSP gave an accurate estimate of DMSPd loss rate constants, leaving the initial DMSPd concentration by SVDF ([DMSPd]SVDF) as a potential source of error for the rate estimates. Indeed, experiments with GF/F filtrate cultures showed that [DMSPd]SVDF is likely to overestimate the bioavailable DMSPd concentration for at least two reasons:1) a significant fraction (10～37%) of DMSP passing through GF/F filters was in particles> 0.2μm and therefore not dissolved, and 2) a significant pool (0.5～1.0 nM) of operationally-dissolved, non-particle DMSP ([DMSPd]