【作者】 厉丞烜；

【导师】 杨桂朋； Ronald P.Kiene；

【作者基本信息】 中国海洋大学 ， 海洋化学， 2010， 博士

【摘要】 二甲基硫(DMS)是参与全球硫循环的最主要的海洋生源硫化物,其在大气中的氧化产物会对全球气候变化和酸雨的形成产生重要影响。二甲基巯基丙酸内盐(DMSP)是DMS的重要前体物质,在DMSP裂解酶的作用下分解产生DMS。生物生产与消费被认为是海洋中DMS和DMSP的主要来源和去除途径,在DMS及DMSP的生物地球化学循环中起着重要作用,决定表层海水中DMS浓度以及海-气通量。因此表层海水中DMS及DMSP生物生产和消费的研究,有助于衡量海洋生物对海水中DMS和DMSP的贡献,进一步深入了解DMS和DMSP的生物地球化学循环过程。本论文首先以受人类活动影响较大的中国半封闭海域北黄海为研究区域,对海水中DMS生物生产和消费速率的时空变化及其影响因素进行系统的研究,初步衡量了此海域表层海水中微生物消费和海-气扩散在DMS去除过程中的相对重要性。其次,通过室内藻类培养实验,研究了中国近海海域常见藻种DMS和DMSP生产释放情况,并探讨了相关理化因子的影响。在美国Mexico海湾沿岸海域,通过35S同位素示踪法,首次评估了溶解态DMSP (DMSPd)的生物可利用率,并定量研究了DMSPd和颗粒态DMSP (DMSPp)生物消费对于DMS生物生产的相对贡献。主要研究结果如下：1.北黄海表层海水中DMS生物生产与消费速率以及相关因素的研究(1)于2006年12月-2007年1月、2007年4-5月和10月对我国北黄海海域表层海水中DMS生物生产和消费速率的时空变化进行了研究。冬季北黄海表层海水中DMS生物生产和消费速率分别为5.41(1.91～13.0)和3.84(0.81～11.6)nM d-1；春季速率分别为6.42(2.38～18.9)和3.71(1.74～13.2)nM d-1；秋季速率分别为7.35(2.04～15.9)和5.67(1.67～13.8)nM d-1。研究表明,北黄海表层海水中DMS生物生产速率在各季节变化趋势为：秋季>春季>冬季,三个季节的平均值为6.39±0.152 nM d-1；而DMS生物消费速率季节变化中,秋季明显高于春、冬两季,三个季节的平均值为4.41±0.249 nM d-1。从空间分布看来,各季节DMS生物生产和消费速率具有相似的空间变化趋势。冬季,DMS生产速率和消费速率在辽东半岛和山东半岛近岸出现高值区,而中部海域则为其低值区。春季,二者的高值区位于靠近辽东半岛东南部的近海海域,在鸭绿江入海口达到最低值。秋季,辽南沿岸区域是DMS生物生产和消费速率高值区,北黄海中部海区的生产和消费速率值则偏低。(2)北黄海表层海水中DMS生物生产与消费过程受现场海洋物理、化学和生物条件(如：温度、盐度、DMSPd和DMS浓度、叶绿素a以及浮游植物组成等)不同程度的影响,是一个复杂的生物地球化学过程。冬季,DMS生物生产速率皆受到各种物理、化学和生物因子的影响,其中Chl a的影响最为显著,其次为海水表层温度和DMSPp浓度。春季和秋季,现场DMSPd和DMSPp浓度对于DMS生物生产速率的影响均较为显著。而对于DMS生物消费速率,冬季和秋季均受到DMS现场浓度的影响,海水表层温度和盐度只在冬季有显著的影响。海水物理、化学和生物因子皆会影响北黄海表层海水中DMS生物生产速率和消费速率,但其影响程度具有明显的季节差异性。(3)北黄海表层海水中DMS生物生产速率皆高于其消费速率,总体平均高出65%,导致DMS净生物生产作用。而且,DMS生产速率和消费速率二者之间存在很好的相关性,表明DMS生物生产与其微生物消费构成一个紧密的生物循环过程。冬季、春季和秋季北黄海表层海水中DMS微生物消耗的生物周转时间τbio分别为0.834(0.2～1.73)、1.59(0.406～4.65)和0.666(0.240～1.36)d；而DMS海—气周转时间τsea-air分别为6.30(0.122～32.3)、5.04(0.868～32.6)和10.0(0.635～56.2)d。冬季、春季和秋季,τsea-air/τbio的比值平均值分别为10.95、3.97、17.94。由此看来,北黄海表层中DMS微生物消耗相对于海—气扩散在DMS迁移转化中的作用更加明显。2.三种海洋浮游微藻的DMS、DMSP生产的研究本文选取了三种中国近海常见藻种,即三角褐指藻(Phaeodactylum tricornutum)、海洋原甲藻(Prorocentrum micans)和球等鞭金藻(8701品系,Isochrysis galbana)为研究对象,通过实验室培养实验研究了这些海洋微藻生长周期内藻体细胞内外DMSP及释放到水体中DMS浓度,并研究了不同盐度、硝酸盐浓度和Fe3+浓度条件对三种微藻DMSP、DMS生产的影响以及硅酸盐浓度对三角褐指藻的影响。结果表明：(1)海洋原甲藻细胞外的DMSP浓度显著高于三角褐指藻和海洋原甲藻的相应浓度。单位生物量内,海洋原甲藻DMSPp含量分别比三角褐指藻高出3个数量级,比球等鞭金藻8701也高出2个数量级。这三种微藻在生长期后期DMS浓度增长速率均较初期明显提高。(2)高硝酸盐浓度抑制海洋原甲藻和三角褐指藻DMSPp的产生；但球等鞭金藻8701的DMSPp生产却不受硝酸盐浓度的影响。海洋原甲藻的DMS生产受[NO3-]影响最为显著,低[NO3-]下DMS/Chl a的比值是高[NO3-]下的7倍。(3)高盐环境能够增强三角褐指藻和海洋原甲藻细胞内DMSP的生产,并促进培养液中DMS生产,而低盐度则明显降低这两种微藻生产DMS的能力。盐度对球等鞭金藻8701细胞内外DMSP产量和DMS生产无明显影响。(4)高[Fe3+]有助于三角褐指藻和海洋原甲藻藻液中DMSPd的形成,降低球等鞭金藻8701中DMSPd的生产。高浓度Fe3+能够促进球等鞭金藻8701细胞内DMSP的合成,却抑制了海洋原甲藻细胞内DMSP的生产。低浓度Fe3+则明显提高海洋原甲藻和球等鞭金藻藻液中DMS的产量；[Fe3+]的变化未对三角褐指藻DMS和DMSPp生产有影响。(5)低硅酸盐浓度条件下三角褐指藻的单位生物量DMSPp浓度高于中高水平硅酸盐条件下的相应浓度,表明低浓度能够有利于其细胞内DMSP的生成。单位生物量DMS生产能力也在低硅酸盐浓度培养液中得到加强,在高于214μM硅酸盐浓度条件下单细胞DMS产量较低且变化不大。3. Mexico海湾沿岸海域DMSPd生物可利用率和周转的评估DMSPd是海洋细菌体内一种重要酶作用有机底物和活性硫气体DMS的前体物质。本研究中,Mexico海湾沿岸海域DMSPd生物消费速率通过两种方法进行测定：一种是借助于DMSP吸收(DMSP-uptake)的抑制剂甘氨酸甜菜碱(GBT)来确定的抑制剂方法,另一种是35S-DMSP示踪的动力学方法。这两种方法都需要确定海水中DMSPd的浓度,其中,DMSPd样品通过Whatman GF/F滤膜(0.7μm)进行小体积重力过滤(SVDF)采集,随即将DMSP进行碱解得到DMS来定量确定DMSPd。其中,35S-DMSP示踪法提供的DMSPd周转速率(35.7～215nM d-1)比GBT抑制剂方法得到的值(0.34～21.6 nM d-1)高出1.7～152倍。进一步实验确定了GBT能够有效抑制DMSPd的降解,而35S-DMSP示踪法能提供准确的DMSPd降解速率常数,这样采用SVDF方法采集测定DMSPd浓度([DMSPd]SVDF)可能是DMSPd降解速率估算的一个潜在的误差来源。的确,GF/F滤液培养实验表明[DMSPd]SVDF可能高估了DMSPd的生物可利用率,这主要有两个原因：(1)在GF/F滤液中,10～37%的DMSP存在于粒径大于0.2μm的颗粒物中,而并非是溶解态的；(2)在真正以溶解态存在的DMSP (DMSPd<0.2μm)中,0.5～1.0 nM的DMSP在几天内难以降解,这部分DMSP占到相应DMSPdsvDF的40～99%。目前,对于这部分难降解的DMSP本质还是未知的。在此研究海域中,所估测的DMSPd浓度非常低,在0.006～1.0 nM范围内,平均值为0.41 nM。本研究建议DMSPd周转和其对于海洋中硫和碳通量的贡献需要重现评估。4. Mexico海湾沿岸海域DMSP生物降解对DMS生物生产的贡献表层海水中,溶解态和颗粒态DMSP都是DMS重要来源,对海洋中DMS生产具有重要的贡献。本研究中,监测Mexico海湾沿岸海域的表层海水及其GF/F滤液中DMS和DMSPd浓度变化趋势,结果发现DMSPd消耗可能促进或不影响DMS的生产。GBT能够短时间内抑制DMSPd的降解,并且此期间GBT能够促进DMSPp降解和DMS生产,而不影响DMS的降解和产率,表明DMSPp对DMS生产具有重要贡献。现场海水的黑暗培养实验中,在忽略DMS光化学和海-气扩散过程的情况下,测定DMS净生产速率、DMSPd消费速率、DMSPd降解为DMS的产率及DMS微生物消费速率,首次定量估算了DMSPp寸于DMS生产的贡献。结果表明来自DMSPd降解的DMS生产速率((DMS生产速率)DMSPd)为0.13～1.72 nM d-1,而来自DMSPp转化的DMS生产速率((DMS生产速率)DMSPp)为2.79～6.82 nM d-1,(DMS生产速率)DMSPp明显高于(DMS生产速率)DMSPd,二者比值在1.84～34.1之间,平均为16.4,充分表明DMSPp才是比DMSPd更重要的DMS来源。此发现有助于更好地认识表层海水中DMS生物生产和消费过程。更多还原

【Abstract】 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]<o.2～m), comprising 40～99% of [DMSPd]svDF, was refractory to degradation on a time scale of days. The nature of this refractory DMSP is currently unknown. We estimated that the bioavailable DMSPd concentrations in our coastal samples were very low (0.006～1.0 nM; mean of 0.41 nM). Our findings call for a reassessment of DMSPd turnover and its contribution to sulfur and carbon fluxes in the ocean. 4. The contribution of DMSP biological consumption on the DMS biological production in the coastal waters of the Gulf of MexicoIn the surface water, DMSP are the major precursor of DMS and the biological turnover of DMSP plays a significant role in DMS production. In the present study, the dark incubations for the surface water sampled from the Gulf of Mexico and the corresponding GF/F filtration are conducted. The variations of DMS and DMSPd during the incubation period demonstrate that the consumption of DMSPd stimulates DMS production or doesn’t influence DMS production. Moreover, GBT inhibits DMSPd consumption effectively and enhances the DMSPp consumption and DMS production. But GBT hasn’t influenced the consumption rates of DMS and DMS yield. Our results indicate the important contribution of DMSPp on DMS production. Furthermore, we measure the rates of net DMS accumulation, as well as the DMSPd consumption rates by the GBT-inhibition approaches. Concurrently, we also establish the DMS production yield from DMSPd and the microbial consumption of DMS by the radio-isotope methods. Subsequently, based on these results, we make the estimates of the DMS production rates from DMSPp with the aim of obtaining a better understanding of the DMS biological production and consumption in the surface ocean and quantitatively assessing the dominant role of DMSPd and DMSPp in the oceanic DMS production. The estimates of (DMS production rate)DMSPd range from 0.13 to 1.72 nM d-1 and (DMS production rate)DMSPp vary between 2.79 and 6.82 nM d-1. Significantly, the estimated DMS production from DMSPp consumption is superior to that from DMSPd degradation by an average factor of 16.4. Herein, relative to the DMSPd, the particulate DMSP seems to be a major source of DMS.更多还原