海洋浮游植物与生物碳汇

系统描述了浮游植物与海洋碳汇相关的几个过程:初级生产、浮游植物沉降、浮游动物粪球打包沉降、经典食物链碳汇、溶解有机碳生产和转化、透明胞外聚合颗粒物(TEP)凝聚网,和CO₂分压升高(海水酸化)影响下浮游植物功能群转变及中国海可能的生物碳汇前景展望。提出海洋初级生产过程和TEP凝聚网过程是中国海生物碳汇的关键过程,而中国海的黄海中部及长江口区域是生物碳汇研究的重点区域,建议将硅藻及其碳汇过程作为今后研究的重点。     

东辽河流域河湖光学吸收特性的季节变化

吸收特性是水体重要的光学特性,也是建立水色反演分析模型的基本参数.本文利用2011年6、9、10月在二龙湖和2012年10月在东辽河的实测数据,通过测定水体营养水平和颗粒物、有色可溶性有机物(CDOM)等光学活性物质的吸收系数,分析了东辽河河湖的光学物质吸收特性和季节变化.结果表明: 二龙湖水体9月处于富营养状态,6月营养水平较低,10月则处于中营养水平;东辽河随采样点位置的差异呈现不同程度的富营养化.水体各组分的吸收系数均随营养水平的增加而逐渐增大.6、10月二龙湖水体总悬浮颗粒物吸收光谱与非色素颗粒物吸收光谱相似,在总吸收中占主导作用的是CDOM;9月总悬浮颗粒物吸收光谱则与浮游植物吸收光谱类似,浮游植物的吸收对总吸收的贡献率最大.6、9月二龙湖浮游植物吸收系数[a_ph(440)]与总磷(TP)呈正相关,6月二龙湖a_ph(440)与溶解有机碳(DOC)呈正相关,非藻类颗粒物吸收系数[a_d(440)]仅与叶绿素a浓度(Chl a)具有相关性.二龙湖(9月)与东辽河a_ph(675)均与Chl a、卡尔森指数(TLI)相关性较好.东辽河流域的河湖水体光学特性存在比较明显的差异:东辽河水体的浮游植物吸收光谱曲线展现出了两种不同类型,浮游植物、非藻类颗粒物、CDOM的贡献率随采样点的不同而相差较大;营养水平较高的9月二龙湖与东辽河水体浮游植物主导了水体光谱吸收,而在二龙湖营养水平较低的月份中(6、10月),颗粒物与CDOM共同主导水体光谱吸收;6月二龙湖与10月东辽河水体CDOM的组成为大分子颗粒物,而9与10月其组成更趋向于小分子颗粒物.     

不同来源和粒径的胶体对光合细菌生长的效应

天然胶体是近岸海域细菌和浮游植物可利用氮的一个重要来源 ,其含量的增加可促进藻类的繁殖和生长 ,有时甚至引发赤潮。研究显示 ,细菌在高分子量胶体存在下的生长和代谢速率比在低分子量中的提高 3～ 6倍 ,暴露在阳光下的胶体有机物可释放生物可利用的富氮组分 ,进而提高细菌对胶体的分解。利用错流超滤技术从河流、河口、海洋水体和微藻培养液中提取胶体 ,研究了胶体来源和粒径对光合细菌 (PSB,沼泽红假单胞菌 Rhodopseudomonaspalustris)生长的影响。结果表明 ,在一定的胶体有机碳浓度范围 ,河流胶体 (0～ 2 81.0μmol/ L )、河口胶体 (0～ 12 1.2μmol/ L )、海洋胶体 (0～ 88.8μmol/ L )和生源胶体 (7.7～5 4 8.6μmol/ L )都能促进 PSB的生长 ,分别使其相对增长率平均提高了 4 7.3%～ 196 .2 % ,3.6 %～ 9.3% ,8.1%～ 10 .4 %和2 .4 %～ 6 .9%。其中 ,PSB在河流胶体中的相对增长率的平均值 (Y)与有机碳浓度 (CDOC)呈对数相关 (Y (% ) =- 193.7 70 .7ln CDOC) ,表明高浓度的河流胶体 ,对 PSB生长的促进效果更显著。两种生源胶体中 ,海水小球藻胶体 (0～ 5 4 8.6μmol/ L )对PSB生长的促进作用大于球等鞭金藻胶体 (7.7～ 384 .4 μmol/ L) ;PSB在粒径为 10 k D～ 0 .2 2 μm的海洋胶体中的生长大于     

藻际环境中胞外聚合物的研究进展

微藻向细胞周围释放营养物质而形成了独特的藻际微环境,吸引了大量细菌的定殖。藻际环境中藻菌关系错综复杂,其间充斥着多样的物质交换与信息交流。以胞外聚合物(extracellularpolymeric substances,EPS)为代表的有机质在其中起着纽带作用。微藻和细菌都可以产生EPS,其过程受多种因素的调节。EPS在藻际环境中具有重要的生态功能,包括参与生物被膜(biofilm)的形成,影响藻菌共生关系的建立以及调节藻际微生物群落组成等。此外,EPS中的一大类别透明胞外聚合物颗粒(transparent exopolymer particles,TEP)还介导了海洋溶解有机碳向颗粒有机碳的转化,参与了海洋碳循环过程。本文以EPS的产生、组成以及对碳转化的影响为重点,综述了其在藻际生态位(Niche)中的生态功能,以期为深入理解藻际环境中的有机质特征和藻菌共生关系提供理论依据。     

颗石藻类群及其生态功能介绍

颗石藻(coccolithophore)是一类在全球海洋中广泛分布的海洋微型浮游植物, 它们在海洋浮游植物功能群落中是一类极其重要的钙化生物类群, 也是海洋中生源无机碳的重要来源, 并且在海洋的碳循环过程中起到重要的作用。颗石藻由于快速增殖而发生水华的过程中能够释放大量的具有挥发性的二甲基硫(DMS)和丙烯酸(acrylic acid), 它们是影响气候变化, 特别是引起区域性环境效应(温室效应)的关键性物质。     

辽河水体光学吸收特性的季节变化

吸收特性是水体重要的光学特性,也是建立生物光学模型的基本参数。利用2013年5月和9月辽河流域水体实测数据对总悬浮颗粒物、浮游植物、非藻类颗粒物以及有色溶解有机物(CDOM)的吸收特性、季节变化进行了研究。研究表明,总颗粒物的吸收光谱曲线与非藻类颗粒物的吸收光谱基本保持一致并且与非藻类颗粒物的吸收[a_d(λ)]以及浮游植物的吸收[a_(ph)(λ)]都呈现显著相关。两个季节,a_d(440)均是总吸收的主要组成部分,CDOM的吸收[a_(CDOM)(440)]则大于a_(ph)(440)的贡献率,但9月a_d(440)的吸收所占比例较5月高。辽河水体非藻类颗粒物中矿物颗粒物的含量较其他一般水体要高。通过分析5月及9月的aph(440)/a_(ph)(675)发现浮游植物中辅助色素与叶绿素a浓度(Chla)的组成季节性变化不大,但其空间特征表现较为明显。另外,CDOM的吸收特性与非藻类颗粒物的吸收相似,呈现出较大的空间差异性;辽河S_(CDOM)基本小于其它河流、湖泊、河口等水体,其CDOM主要由大分子物质组成。     

铁施肥促进海洋浮游植物和生物碳泵的不确定性

铁作为浮游植物所必需的微量元素,限制了全球超过三分之一海域的初级生产力,尤其是在高营养盐、低叶绿素海域(high nutrient low chlorophyll,HNLC)。长期以来海洋铁施肥被认为是一项可以降低大气二氧化碳含量的地球工程策略。然而通过13次海洋人工铁施肥(artificial ocean iron fertilization,aOIF)实验发现,铁的额外添加对海洋深层碳输出量的促进作用要显著低于预期。本文简要地总结了碳在海洋和大气中的循环过程,回顾了人工铁施肥实验对生物碳泵和碳通量等的影响,分析了从海洋铁施肥到海洋碳汇关键生物地球化学过程的影响因素。综上分析发现,科学界对生物碳泵过程及其调控机制的认识仍十分浅薄,考虑到海洋铁施肥还会对海洋生态系统带来一定的负面作用,铁施肥能否作为降低大气中CO₂的有效手段,以达到碳中和并缓解温室效应仍需进一步研究。     

“海蜇-缢蛏-牙鲆-对虾”混养池塘悬浮颗粒物结构及其有机碳库储量

为了阐明"海蜇-缢蛏-牙鲆-中国对虾"混养池塘生态系统的结构和功能特征,并为不同养殖模式的碳循环研究和发展低碳渔业提供参考,于2013年5—10月对辽宁丹东东港地区(N 39°51';E 124°09')两个该种混养池塘的悬浮颗粒物结构及其有机碳储量进行了研究。结果表明,两个实验池塘总悬浮颗粒物含量分别为(67.12±6.03)mg/L和(70.05±7.63)mg/L,其中无机悬浮颗粒物占总悬浮颗粒物的72.57%和75.49%;有机悬浮颗粒物占总悬浮颗粒物的27.43%和24.51%。有机悬浮颗粒物中,腐质及细菌占总悬浮颗粒物的27.15%和24.20%;浮游植物干重占0.15%和0.22%;浮游动物干重占0.13%和0.09%。两个实验池塘悬浮颗粒物中的总有机碳(TOC)含量分别为(7.31±1.51)mg/L和(6.42±1.31)mg/L;其中溶解有机碳(DOC)占总有机碳的76.33%和70.56%;颗粒有机碳(POC)占总有机碳的23.67%和29.44%;细菌碳占总有机碳的7.96%和7.18%;腐质碳占总有机碳的14.70%和20.90%;浮游植物碳占总有机碳的0.56%和0.95%;浮游动物碳占总有机碳的0.45%和0.41%。实验池塘中总悬浮颗粒物含量相对较高,其中无机悬浮颗粒物是主要的组成部分;细菌和腐质是有机悬浮颗粒物主要的组成部分,说明腐质链在该种养殖生态系统的物质循环和能量流动中起主要作用。     

全球CO2 水平升高对浮游植物生理和生态影响的研究进展

工业革命以来由于化石燃料的大量燃烧,大气CO₂水平不断增加,预计在21世纪末将增至现有水平的两倍,达到750 μL/L。作为全球初级生产力的重要贡献者,浮游植物应对CO₂水平升高的生理生态响应必然会对水生生态系统和碳、氮等元素的生物地球化学循环产生重要影响。全球CO₂水平的升高将显著改变水体的碳化学环境,淡水生态系统(湖泊和河流)由于容量小变化比海洋更为显著。水体碳化学环境的改变首先会影响浮游植物个体,在高CO₂水平下,浮游植物的细胞会有变小的趋势,并且细胞的光合作用强度也会有不同程度的增加,其中细胞较小或者不具有碳浓缩机制(CCM)的浮游植物增加较多,此外浮游植物细胞的化学元素计量值也将显著改变。随后浮游植物个体水平上的变化会进一步影响水生生态系统,例如水体初级生产力水平的提高,浮游植物、浮游动物群落结构组成以及水体微食物网结构的变化等。此外浮游植物对CO₂水平升高的生理生态响应程度还与水体的营养水平有关。总结了大气CO₂水平升高对浮游植物生理生态影响的研究方法,展望了未来可能的研究方向。     

一氧化氮(NO)对海洋浮游植物的作用

该文介绍海洋浮游植物内源一氧化氮(NO)的产生,NO对海洋浮游植物生长的作用,以及有关NO在海洋浮游植物环境胁迫响应中生理作用的研究现状,并对与这些问题相关的研究趋势作了分析和讨论。     

Does the marine copepod Calanus pacificus consume transparent exopolymer particles (TEP)?

Gel-like transparent exopolymer particles (TEP) formed frompolysaccharides exuded copiously by natural phytoplankton andbacteria occur ubiquitously in sea water, but the utilizationof these particles as a food source by zooplankton is poorlyknown. The common marine calanoid copepod Calanus pacificusconsumed TEP and produced abundant fecal pellets when TEP wereoffered both alone and in the presence of diatom cells. TEPconsumption increased with TEP concentration and the presenceof TEP did not inhibit ingestion of cells. However, becauseof their low carbon content, TEP contributed only 15% to totalcarbon consumption in the presence of phytoplankton food. Whilecopepods consumed pure TEP in this study, sticky TEP in naturecontain abundant inclusions of bacteria and microorganisms toosmall for copepods to capture individually. Thus, consumptionof TEP may be most significant as a mechanism by which carbonmay be shunted from the microbial loop to higher trophic levels.     

Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.     

Abundance, size distribution and bacterial colonization of transparent exopolymeric particles (TEP) during spring in the Kattegat

The abundance, size distribution and bacterial colonizationof transparent exopolymeric particles (TEP) were monitored inthe Kattegat (Denmark) at weekly intervals throughout the spring(February-May) encompassing the spring diatom bloom. These recentlydiscovered particles are believed to be formed from colloidalorganic material exuded by phytoplankton and bacteria, and mayhave significant implications for pelagic flux processes. Duringthis study, the number concentration of TEP (>1 µm)ranged from 3 x 10³ to 6 x 10⁴ ml^–1 and the volume concentrationbetween 0.3 and 9.0 p.p.m.; they were most abundant in the surfacewaters subsequent to the spring phytoplankton bloom. The rangeof TEP (encased) volume concentration was similar to that ofthe phytoplankton, although at times TEP volume concentrationexceeded that of the phytoplankton by two orders of magnitude.The TEP size distribution followed a power law, with the abundanceof particles scaling with particle diameter^–(ß+1).The seasonal average estimate of ß (2.3) was not significantlydifferent from three, consistent with TEP being formed by shearcoagulation from smaller particles. However, date-specific estimatesof ß differed significantly from three, probably becauseTEP are fractal. All TEP were colonized by bacteria, and bacteriawere both attached to the surface of and embedded in TEP. Yetthe number of attached bacteria per TEP was related neitherto the surface area nor the volume, but rather scaled with TEPsize raised to an exponent of     

Inhibition of copepod feeding by exudates and transparent exopolymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community

We investigated if (1) dissolved compounds excreted by Phaeocystis globosa and (2) transparent exopolymer particles (TEP) formed from carbohydrates excreted into the water affect the feeding of nauplii and females of the calanoid copepod Temora longicornis during a P. globosa bloom. Copepod grazing on the diatom Thalassiosira weissflogii in the presence of these possible grazing deterrents was measured during three successive weeks of a mesocosm study, simulating the development of a P. globosa bloom. Our results demonstrate no indication for the presence of feeding deterrents in the dissolved phase, but a strong inhibitory effect of transparent exopolymer particles (TEP) on the consumption of algae by both nauplii and adult copepods. The inhibitory effect of TEP was connected to the accumulation of DOM during the progress of the bloom. We suggest that a reduction in the grazing pressure of zooplankton may increase the survival of the liberated single cells during disruption of colonies and allow seeding populations to persist. Furthermore, P. globosa reduces the trophic efficiency of the food web not only by withdrawal of its colonies from grazing but also by a relaxation of the grazing pressure on co-occurring phytoplankton and by alteration of the food web structure via TEP production.     

Viral lysis of Micromonas pusilla: impacts on dissolved organic matter production and composition

The viral mediated transformation of phytoplankton organic carbon to dissolved forms (“viral shunt”) has been suggested as a major source of dissolved organic carbon (DOC) in marine systems. Despite the potential implications of viral activity on the global carbon fluxes, studies investigating changes in the DOC composition from viral lysis is still lacking. Micromonas pusilla is an ecologically relevant picoeukaryotic phytoplankter, widely distributed in both coastal and oceanic marine waters. Viruses have been found to play a key role in regulating the population dynamics of this species. In this study we used axenic cultures of exponentially growing M. pusilla to determine the impact of viral lysis on the DOC concentration and composition, as estimated from lysate-derived production of transparent exopolymer particles (TEP) and two fractions of fluorescent dissolved organic matter (DOM): aromatic amino acids (excitation/emission; 280/320 nm; F(280/320)) and marine humic-like fluorescent DOM (320/410 nm; F(320/410)). DOC concentration increased 4.5 times faster and reached 2.6 times higher end concentration in the viral infected compared with the non-infected cultures. The production of F(280/320) and F(320/410) were 4.1 and 2.8 times higher in the infected cultures, and the elevated ratio between F(280/320) and F(320/410) in lysates suggested a higher contribution of labile (protein) components in viral produced DOM than in algal exudates. The TEP production was 1.8 times faster and reached a 1.5 times higher level in the viral infected M. pusilla culture compared with the non- infected cultures. The measured increase in both DOC and TEP concentrations suggests that viral lysis has multiple and opposite implications for the production and export processes in the pelagic ocean: (1) by releasing host biomass as DOC it decreases the organic matter sedimentation and promotes respiration and nutrient retention in the photic zone, whereas (2) the observed enhanced TEP production could stimulate particle aggregation and thus carbon export out of the photic zone.     

Production of transparent exopolymer particles (TEP) by benthic suspension feeders in coastal systems

In the marine environment, transparent exopolymer particles (TEP) are ubiquitous and abundant, playing a significant role in carbon cycling and the structuring of food webs. Previous studies have shown that phytoplankton, bacteria, and oysters contribute to the production of TEP through the release of exopolymers. However, little is known about other potential sources of TEP and TEP precursors, especially in coastal systems. It was hypothesized that suspension feeders contribute to the TEP pool in near-shore environments through the release of exopolymers in both the dissolved and particulate form, and tested these hypotheses in both laboratory and field experiments. In the laboratory, the production of TEP by several species of benthic suspension feeders (the blue mussel, Mytilus edulis; the bay scallop, Argopecten irradians; the slipper snail, Crepidula fornicata; and the solitary ascidians, Ciona intestinalis and Styela clava) was investigated from October to November 2002 and June 2003. Concentrations of TEP and DOC were determined by spectrophotometry after alcian blue staining and high-temperature, catalytic oxidation, respectively. Similar analyses were conducted on water samples from the field in July 2003, collected in close proximity to dense beds of mussels in the Poquonnock River, Connecticut, USA (41°19′ N, − 72°02′ W). Laboratory results indicated that actively-pumping blue mussels, bay scallops, slipper snails, and both species of solitary ascidians significantly enhanced TEP concentrations above background levels over a five-hour period. However, only the solitary tunicate S. clava significantly enhanced DOC concentrations above background levels over the same period of time. Field samples indicated that TEP and DOC concentrations were high in close proximity to dense beds of mussels. These results imply that a variety of benthic suspension feeders produce TEP during feeding activities which could lead to enhanced flocculation of organic matter and carbon deposition in near-shore waters.     

Coupling between autocatalytic cell death and transparent exopolymeric particle production in the marine cyanobacterium Trichodesmium

Extracellular polysaccharide aggregates, operationally defined as transparent exopolymeric particles (TEP), are recognized as an important conduit for carbon recycling and export in aquatic systems. Yet, the factors controlling the build-up of the TEP pool are not well characterized. Here we show that increased TEP production by Trichodesmium, an oceanic bloom-forming nitrogen-fixing (diazotrophic) cyanobacterium, is coupled with autocatalytic programmed cell death (PCD) process. We demonstrate that PCD induction, in both laboratory cultures and natural populations, is characterized by high caspase-like activity, correlates with enhanced TEP production, and occurs under iron and phosphorus starvation, as well as under high irradiance and oxidative stress. Enhanced TEP production was not observed in actively growing populations. We provide further evidence that iron is a key trigger for the induction of PCD. We demonstrate, for the first time, the concomitant enhanced build-up of the TEP pool when Trichodesmium is Fe-stressed. These results suggest a functional linkage between activation of caspases and PCD in Trichodesmium and regulation of vertical carbon and nitrogen fluxes. We hypothesize that modulation of TEP formation and its qualities by different mortality pathways could regulate the fate of phytoplankton blooms and particulate organic matter in aquatic ecosystems.