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Production of transparent exopolymer particles from two marine diatoms and its ecological significance

  • Received Date: 2019-03-04
    Accepted Date: 2019-04-03
  • The transparent exopolymer particles(TEP), a kind of transparent colloidal particulate matter, consists of extracellular polysaccharides. TEP is of great significance to the carbon cycle of marine ecosystems. In this study, two marine diatoms, Ditylume brightwelii and Chaetoceros affinis, were studied. The TEP concentration, the relationship between TEP and Chlorophyll a (Chl a) and the C∶N ratio of TEP were studied at different growth phases. The results showed that TEP was produced by both species during the whole growth phases, and TEP concentration was different in different growth phase. The maximum TEP concentration of D. brightwelii and C. affinis was produced in the exponential phase and the decline phase, respectively. The maximum TEP concentration per cell volume and per Chl a of C. affinis was 184.91±14.03 fg Xeq/μm3 and 38.06±4.96 μg Xeq./μg Chl a, and were 16 and 5 times higher than the values obtained from the D. brightwelii. The analysis of the relationship between Chl a and TEP in two diatoms showed that the function relationship between TEP=α (Chl a) β was presented in the exponential phase (D. brightwelii: R2=0.98; C. affinis: R2=0.80). The TEP C∶N ratio of both diatoms was higher than the Redfield ratio (C∶N=106∶16). It indicates that the generation of TEP was difference between species, and the growth phase significantly affects the efficiency of TEP production. The high carbon concentration of TEP show that TEP production contributes significantly to the ocean carbon cycle.
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  • [1] ALLDREDGE A L, PASSOW U, LOGAN B E. The abundance and significance of a class of large, transparent organic particles in the ocean[J]. Deep Sea Research Part I: Oceanographic Research Papers, 1993, 40(6): 1131-1140. doi: 10.1016/0967-0637(93)90129-Q
    [2] LOGAN B E, PASSOW U, ALLDREDGE A L, et al. Rapid formation and sedimentation of large aggregates is predictable from coagulation rates (half-lives) of transparent exopolymer particles (TEP)[J]. Deep Sea Research Part II: Topical Studies in Oceanography, 1995, 42(1): 203-214. doi: 10.1016/0967-0645(95)00012-F
    [3] ENGEL A, PASSOW U. Carbon and nitrogen content of transparent exopolymer particles (TEP) in relation to their Alcian Blue adsorption[J]. Marine Ecology Progress Series, 2001, 219: 1-10. doi: 10.3354/meps219001
    [4] PASSOW U. Transparent exopolymer particles (TEP) in aquatic environments[J]. Progress in Oceanography, 2002, 55(3/4): 287-333.
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    [7] PASSOW U. Production of transparent exopolymer particles (TEP) by phyto-and bacterioplankton[J]. Marine Ecology Progress Series, 2002b, 236: 1-12. doi: 10.3354/meps236001
    [8] THORNTON D C O. Diatom aggregation in the sea: mechanisms and ecological implications[J]. European Journal of Phycology, 2002, 37(2): 149-161. doi: 10.1017/S0967026202003657
    [9] TSUTSUMI H, OKAMURA E, OGAWA M, et al. Studies of the cross section of water in the innermost areas of Ariake Bay with the recent occurrence of hypoxic water and red tide[J]. Oceanography in Japan, 2003, 12(3): 291-305. doi: 10.5928/kaiyou.12.291
    [10] FUKAO T, KIMOTO K, KOTANI Y. Production of transparent exopolymer particles by four diatom species[J]. Fisheries Science, 2010, 76(5): 755-760. doi: 10.1007/s12562-010-0265-z
    [11] 孙翠慈, 王友绍, 吴梅林, 等. 夏季珠江口透明胞外聚合颗粒物分布特征[J]. 熱帶海洋學報, 2010, 29(5): 81-87.
    [12] 彭安国, 黄奕普. 九龙江河口区TEP及其与铀、钍、钋同位素相关性的研究[J]. 厦门大学学报: 自然科学版, 2007, 46(S1): 38-42.
    [13] PASSOW U, ALLDREDGE A L. A dye‐binding assay for the spectrophotometric measurement of transparent exopolymer particles (TEP)[J]. Limnology and Oceanography, 1995, 40(7): 1326-1335. doi: 10.4319/lo.1995.40.7.1326
    [14] ABDULLAHI A S, UNDERWOOD G J C, GRETZ M R. Extracellular matrix assembly in diatoms (bacillariophyceae). v. environmental effects on polysaccharide synthesis in the model diatom, Phaeodactylum tricornutum[J]. Journal of Phycology, 2006, 42(2): 363-378. doi: 10.1111/jpy.2006.42.issue-2
    [15] URBANI R, MAGALETTI E, SIST P, et al. Extracellular carbohydrates released by the marine diatoms0 Cylindrotheca closterium, Thalassiosira pseudonana and Skeletonema costatum: Effect of P-depletion and growth status[J]. Science of the Total Environment, 2005, 353(1/2/3): 300-306.
    [16] BOOTH B C, LAROUCHE P, BÉLANGER S, et al. Dynamics of Chaetoceros socialis blooms in the North Water[J]. Deep Sea Research Part II: Topical Studies in Oceanography, 2002, 49(22/23): 5003-5025.
    [17] MARI X, RASSOULZADEGAN F, BRUSSAARD C P D, et al. Dynamics of transparent exopolymeric particles (TEP) production by Phaeocystis globosa under N- or P-limitation: a controlling factor of the retention/export balance[J]. Harmful Algae, 2005, 4(5): 895-914. doi: 10.1016/j.hal.2004.12.014
    [18] CHEN J. FACTORS AFFECTING CARBOHYDRATE PRODUCTION AND THE FORMATION OF TRANSPARENT EXOPOLYMER PARTICLES (TEP) BY DIATOMS[D]. College Station,Texas: TEXAS A & M UNIVERSITY, 2014:1-249.
    [19] BERMAN-FRANK I, ROSENBERG G, LEVITAN O, et al. Coupling between autocatalytic cell death and transparent exopolymeric particle production in the marine cyanobacterium Trichodesmium[J]. Environmental Microbiology, 2007, 9(6): 1415-1422. doi: 10.1111/emi.2007.9.issue-6
    [20] SPUNGIN D, BELKIN N, FOSTER R A, et al. Programmed cell death in diazotrophs and the fate of organic matter in the western tropical South Pacific Ocean during the OUTPACE cruise[J]. Biogeosciences, 2018, 15(12): 3893-3908. doi: 10.5194/bg-15-3893-2018
    [21] THORNTON D C O, CHEN J. Exopolymer production as a function of cell permeability and death in a diatom (Thalassiosira weissflogii) and a cyanobacterium (Synechococcus elongatus)[J]. Journal of Phycology, 2016, 53(2): 245-260.
    [22] MARI X. Carbon content and C:N ratio of transparent exopolymeric particles (TEP) produced by bubbling exudates of diatoms[J]. Marine Ecology Progress, 1999, 183: 59-71. doi: 10.3354/meps183059
    [23] PASSOW U, SHIPE R F, MURRAY A, et al. The origin of transparent exopolymer particles (TEP) and their role in the sedimentation of particulate matter[J]. Continental Shelf Research, 2001, 21(4): 327-346. doi: 10.1016/S0278-4343(00)00101-1
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    沈阳化工大学材料科学与工程学院 沈阳 110142

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Production of transparent exopolymer particles from two marine diatoms and its ecological significance

  • 1. Research Center for Harmful Algal and Marine Biology, Jinan University, Guangzhou 510632, China
  • 2. South China Sea Institute of Marine Planning and Environmental Research, State Oceanic Administration, Guangzhou 510300, China
  • 3. Fourth institute of oceanography, Ministry of Natural Resources, Beihai 536002, China
  • 4. China Association of Marine Affairs, Beijing 100194, China

Abstract: The transparent exopolymer particles(TEP), a kind of transparent colloidal particulate matter, consists of extracellular polysaccharides. TEP is of great significance to the carbon cycle of marine ecosystems. In this study, two marine diatoms, Ditylume brightwelii and Chaetoceros affinis, were studied. The TEP concentration, the relationship between TEP and Chlorophyll a (Chl a) and the C∶N ratio of TEP were studied at different growth phases. The results showed that TEP was produced by both species during the whole growth phases, and TEP concentration was different in different growth phase. The maximum TEP concentration of D. brightwelii and C. affinis was produced in the exponential phase and the decline phase, respectively. The maximum TEP concentration per cell volume and per Chl a of C. affinis was 184.91±14.03 fg Xeq/μm3 and 38.06±4.96 μg Xeq./μg Chl a, and were 16 and 5 times higher than the values obtained from the D. brightwelii. The analysis of the relationship between Chl a and TEP in two diatoms showed that the function relationship between TEP=α (Chl a) β was presented in the exponential phase (D. brightwelii: R2=0.98; C. affinis: R2=0.80). The TEP C∶N ratio of both diatoms was higher than the Redfield ratio (C∶N=106∶16). It indicates that the generation of TEP was difference between species, and the growth phase significantly affects the efficiency of TEP production. The high carbon concentration of TEP show that TEP production contributes significantly to the ocean carbon cycle.

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  • 透明胞外聚合颗粒物(transparent exopolymer particles,TEP)是一类由胞外多糖组成的透明胶状物质[1],具有高黏性[2]、高碳氮比[3]等特点。TEP能黏附溶解有机物、细菌、碎屑或微型浮游植物等形成不同粒径的聚集体,构成独特的物理化学环境,可供微生物栖息[4]。TEP会给微生物提供丰富的碳源,细菌分解利用后,将碳源传递给更高营养级,所以TEP可直接参与微食物环的组成。此外,不同粒径的聚集体能直接被浮游动物、鱼类或其他海洋动物摄食,这样溶解有机物、细菌等就可借助TEP的黏附作用进入传统食物网,TEP是微食物环与传统食物链连接的核心[4]。TEP可加快小型颗粒物转化成大型颗粒物的速率,使海表层颗粒物聚集形成致密性高、结构稳定、易沉降的海洋雪,从而缩短颗粒物沉降至深海的时间[4-5]。在沉降过程中,TEP进一步吸附周围水体中的碳元素,增加向下输送的碳量,将更多的碳封存在海底,对大气CO2浓度起到反馈调节作用[6]。因此,TEP被认为是海洋生态系统碳循环的重要组成部分。

    硅藻在生长繁殖过程中会向细胞外释放大量多糖,这些胞外多糖通过起泡或凝结的方式自发组装形成TEP[1]。因此,当发生以硅藻为主的水华时,通常会伴随高浓度TEP的产生,使得海表层大量细胞积聚形成胶状聚集体[7-8]。但有些硅藻水华在爆发的高峰期并不会立即出现聚集体,而是延滞至水华的衰退阶段[9]。研究发现,这种现象与不同硅藻种类在不同生长时期所产TEP含量的差异相关,如刚毛根管藻(Rhizosolenia setigera)在衰亡期前产生的TEP含量很低,仅有1×103~2×103 μg Xeq./L,在衰亡期则产生高浓度的TEP,约为2.2×104~2.3×104 μgXeq./L;而格氏圆筛藻(Coscinodiscus granii)在整个生长周期内均会产生高浓度的TEP,约为5×103~15×103 μg Xeq./L[10]

    目前我国关于硅藻在不同生长时期产生TEP的室内研究较少,主要集中在现场调查方面,如调查珠江口[11]、九龙江河口[12]等海域的TEP分布特征。现场研究发现微型浮游植物可能比小型浮游植物对TEP的贡献更大[11]。所以本文拟选取粒径相差较大的两种硅藻布氏双尾藻(Ditylume brightwelii)和窄隙角毛藻(Chaetoceros affinis)为研究对象,重点研究两种硅藻在不同生长时期产生TEP的含量并比较两者产生TEP的效率、TEP与Chl a的关系以及TEP C∶N比。旨在阐明:(1)两种硅藻产生TEP是否具有种间差异性;(2)TEP与浮游植物的关系;(3)TEP对海洋碳循环的贡献。

1.   材料与方法

    1.1.   材料

  • 选用两种海洋硅藻为研究对象(表1)。布氏双尾藻采自珠海海域,窄隙角毛藻采自香港青衣海域,均保存于暨南大学赤潮与海洋生物学研究中心。两种硅藻均用f/2培养基培养,培养温度(20±1) ℃,盐度 30±1,光照强度100 μmol photons./m2·s,光循环12 h:12 h。

    实验藻种等效球体直径ESD /μm细胞体积/×103 μm3·cell-1采集地
    布氏双尾藻(Ditylume brightwelii75.11±16.5861.30±14.85中国珠海
    窄隙角毛藻(Chaetoceros affinis15.29±1.831.12±0.41中国香港

    Table 1.  The equivalent spherical diameter (ESD), cell volume and collection site of the two diatoms

  • 1.2.   实验方法

  • 布氏双尾藻和窄隙角毛藻的初始细胞密度均为100 cells/mL。为了消除细菌的影响,分别加入终浓度为0.04 μg/mL的青霉素、终浓度为0.01 μg/mL的硫酸链霉素。培养在2 L锥形瓶中,培养体积为1600 mL,设置3个平行样,每天取样计数细胞密度,测定Chl a浓度,每隔1 d测定TEP含量、C∶N比。

    取样与计数:取样前,轻轻摇晃锥形瓶使硅藻细胞分布均匀,每个瓶中取出5mL样品,加入酸性Lugols’s溶液固定。在OLYMPUS-CKX41倒置显微镜下,利用1 mL计数框计数细胞密度。

    Chl a浓度测定:每次取30mL藻液,将其过滤到GFF膜上,将滤膜转移至离心管中,加入5 mL 90%丙酮后旋涡震荡10 s,在4 ℃黑暗下萃取12 h,4000 rpm转速下离心20 min,用紫外可见分光光度计测出上清液在750、663、645、630 nm处的吸光值。通过以下公式计算得出Chl a浓度:

    式中:C(Chl a)为Chl a浓度;V1为丙酮萃取液体积;V2为藻液体积;D750、D663、D645和D630为对应波长下的吸光值;L为比色皿光程。

    TEP含量测定:每次取3 mL藻液,用孔径0.4 μm的聚碳酸酯滤膜过滤,过滤负压≤0.02 MPa。加入1 mL 0.02%的爱尔新蓝(pH=2.5,含0.06%乙酸)进行染色。随后用1 mL超纯水洗涤两次。将滤膜转移至25 mL烧杯中,加入6 mL 80%的H2SO4溶液,浸泡2 h。然后用紫外可见分光光度计在波长787 nm下测定溶液吸光值,用黄原胶标准曲线计算出TEP含量。TEP含量以黄原胶(Xeq)的量来表示[13]

    TEP的C∶N测定:每次取45 mL藻液,在6000 rpm下离心20 min。取30 mL上清液,用孔径为0.7 μm的GFF膜过滤。将膜用锡箔纸包裹,40 ℃下烘干48 h。随后用0.5 mol/L 的HCl酸化。再次40 ℃下烘干24 h,装入锡舟中。利用元素-稳定同位素比值质谱仪测定得到C∶N比值。

  • 1.3.   统计分析方法

  • 应用Origin 2017对数据进行处理与作图,应用SPSS 25.0软件对数据进行统计分析,利用one way-ANOVA对不同生长时期的TEP含量进行显著性分析,显著性水平设置为P<0.05。

2.   结果与讨论

    2.1.   结果

    2.1.1.   生长与TEP
  • 两种硅藻在不同生长时期的TEP含量不同,具有极显著性差异(P<0.001)。布氏双尾藻TEP含量在指数期(Ⅱ)会伴随着细胞密度的增加而增加,在稳定期(Ⅲ)达到最大值1335.37±229.53 μg Xeq./L,随后细胞开始衰亡,TEP含量也逐渐减少(图1 A)。相反,窄隙角毛藻TEP含量在整个生长周期内均逐渐增加,不随细胞的衰亡而减少,甚至在衰亡期(Ⅳ)出现急剧增加的现象,达到了6031.25±433.48 μg Xeq./L,为布氏双尾藻最大TEP含量的5倍(图1 B)。

    Figure 1.  The change of TEP concentration with cell growth(Ⅰ:Lag phase;Ⅱ:Exponential phase;Ⅲ:Stationary;Ⅳ:Decline phase)

    将TEP含量归一化为单位细胞体积、单位Chl a含量来比较两种硅藻产TEP的效率(图2)。结果显示,窄隙角毛藻比布氏双尾藻产TEP的效率更高。在整个生长周期内,布氏双尾藻单位体积TEP含量与单位Chl a TEP含量变化趋势相同(图2 AB),均在指数期达到最大值,分别为11.66±2.47 fg Xeq./μm3、7.67±1.65 μg Xeq./μg Chl a,进入稳定期后均逐渐减少。窄隙角毛藻单位细胞体积TEP含量在指数期和稳定期均增加较缓慢(图2 C),在衰亡期急剧增加,达到最大值184.91±14.03 fg Xeq./μm3,是布氏双尾藻单位细胞体积所产最大TEP含量的16倍;而归一化为单位Chl a的TEP 含量在指数期和衰亡期均较高(图2 D),分别为34.68±5.37 μg Xeq./μg Chl a,38.06±4.96 μg Xeq./μg Chl a,约为布氏双尾藻单位Chl a所产最大TEP含量的5倍。

    Figure 2.  Changes in concentration TEP of volume per cell and chlorophyll a per unit in different growth phase(Ⅰ:Lag phase;Ⅱ:Exponential phase;Ⅲ:Stationary;Ⅳ:Decline phase)

    上述结果表明TEP会随细胞生长时期而发生动态变化。这也可通过显微镜验证(图3):在指数期,主要观察到布氏双尾藻与窄隙角毛藻的细胞生长状态好,细胞完整性高,细胞表面附着大量胞外多糖(图3AB),说明细胞将大量固定的碳以多糖的形式向胞外释放,从而形成TEP。在衰亡期,主要观察到两种硅藻细胞生长状态较差,细胞均有破损(图3CD),相比窄隙角毛藻的细胞破损程度更高,导致细胞内存储的颗粒性多糖以TEP的形式泄露(图3 D)。

    Figure 3.  Schematic diagram of two diatoms stained with alcian blue

  • 2.1.2.   TEP与Chl a的关系
  • 两种硅藻在不同生长时期所产TEP含量与Chl a含量的关系不同,仅在指数期能用Chl a含量来表征TEP含量。在指数期,两种硅藻的TEP含量与Chl a含量呈现出TEP=α(Chl aβ的函数关系(图4),而在其他生长时期这种函数关系不存在。在函数关系中(图4),布氏双尾藻的β值接近于1,所以其拟合曲线趋近于一条直线,表明TEP含量会随Chl a含量的增加而增加。但窄隙角毛藻的β值较小,表明在指数期随着Chl a含量的增大其细胞产TEP的速率会有所减缓,这与指数后期窄隙角毛藻单位Chl a的TEP产量研究结果相符(图2 D)。

    Figure 4.  The function relationship between TEP concentration and chlorophyll a concentration in the exponential growth phase of two diatoms

  • 2.1.3.   C∶N
  • 两种硅藻产生的TEP均含有高浓度的碳(表2),且窄隙角毛藻高于布氏双尾藻。在整个生长周期内,布氏双尾藻和窄隙角毛藻的TEP C∶N均高于Redfield比值(C∶N=106∶16)(表2)。在衰亡期,窄隙角毛藻的TEP C∶N甚至达到Redfield比值的2倍,布氏双尾藻TEP的 C∶N约为Redfield C∶N比值的1.5倍。

    生长时期C∶N(mol∶mol)
    C. affinisD. brightwelii
    10.02±2.218.40±1.39
    11.42±2.339.38±1.32
    11.47±0.899.48±1.92
    12.98±2.809.85±1.98

    Table 2.  The C∶N ratios of TEP in diatom culture solution at different growth phase

  • 2.2.   讨论

  • 研究表明,海洋生态系统中浮游植物产生TEP会随生长时期和物种种类的不同而不同。如三角褐指藻(Phaeodactylum tricornutum)、新月柱鞘藻(Cylindrotheca closterium)、格氏圆筛藻(Coscinodiscus granii)的TEP主要产生于指数期,而中肋骨条藻(Skeletonema costatum )、刚毛根管藻(Rhizosolenia setigera)的TEP主要产生于衰亡期[10, 14-15]。本研究结果同样显示,两种硅藻在不同生长时期产生的TEP含量不同,说明两种硅藻产生TEP具有种间差异性。

    窄隙角毛藻单位细胞体积、单位Chl a所产TEP分别是布氏双尾藻相应单位TEP含量的16倍和5倍。由此说明,窄隙角毛藻比布氏双尾藻产TEP的效率更高,属于微型浮游植物的窄隙角毛藻会将细胞内固定的碳更多以胞外多糖的形式向水体中释放。这与孙翠慈等人在我国珠江口发现微型浮游植物(粒径3~20 μm)可能比小型浮游植物(20~200 μm)对TEP贡献更大的结论相符[11]。Booth等[16]在现场海区发现角毛藻属能比其他硅藻产生更黏更大的有机聚集体。此外,本研究结果也与Passow等[7]在比较了指数期窄隙角毛藻、威氏海链藻和有棱棱形藻(Nitzschia angularis)等种类后得出的结论一致;但Passow的研究并未测定稳定期和衰亡期的TEP含量,本研究发现窄隙角毛藻在衰亡期含量急剧增加,显著高于指数期的TEP含量。该结果能解释为什么在水华的衰退阶段会出现大量黏液和鱼类死亡等现象,因为衰亡期高浓度的TEP能凝聚浮游植物、碎屑等颗粒物形成大片的胶状聚集体,使海-气交换通量下降,从而导致鱼类缺氧死亡。

    浮游植物TEP的形成方式有两种:一是浮游植物主动向细胞外释放胞外多糖,这些胞外多糖通过凝结或起泡等物理方式形成TEP[4];二是由浮游植物细胞内所固定颗粒碳的泄漏而形成,与细胞的生长状态和环境因素有关[17-18]。本研究结果显示布氏双尾藻单位细胞体积和单位Chl a产TEP均在指数期最高,在衰亡期较低;而窄隙角毛藻所产TEP在指数期和衰亡期均较大。通过显微镜观察也发现,在衰亡期窄隙角毛藻细胞破损严重会泄露多糖,而布氏双尾藻相对较低。所以布氏双尾藻的TEP可能主要通过健康细胞向胞外释放多糖而形成;窄隙角毛藻产TEP更倾向来源于衰亡细胞破碎泄露细胞内颗粒多糖。Fukao等研究发现,呈链状生长的中肋骨条藻细胞在衰亡期会断裂破碎释放大量TEP[10],与本研究的链状窄隙角毛藻结果相似。此外,大量研究显示许多微生物也会通过泄露、胞外作用或程序性死亡来释放TEP[19-20]。Thornton等[21]研究发现,在营养盐限制或氧化应激反应下嗜热蓝藻(Synechococcus elongatus)和威氏海链藻细胞程序性死亡后,TEP的产量增加。因此,TEP可由浮游植物裂解泄露的胶体和溶解多糖通过非生物的方式形成,细胞的程序性死亡可能是TEP产生的来源之一。

    本研究发现两种硅藻在指数期TEP含量与Chl a含量存在函数关系TEP=α(Chl aβ,同Passow等[7]的研究结果相同,他们发现6种浮游植物在生长阶段也具有该函数关系,且β的值均<1,本文布氏双尾藻和窄隙角毛藻的β值分别为0.93、0.30,均小于1。在衰亡期此函数关系消失,这种现象可能归因于在衰亡期,TEP会随着细胞的裂解而增加,或随着细菌的分解而减少,或细胞为了生长繁殖而将碳储存在细胞内,从而减少多糖的分泌;而Chl a则一定会随着细胞的衰亡而逐渐减少。由此证明,在指数期,Chl a可能直接对TEP产量产生影响,在海洋生态系统中浮游植物对TEP的形成起着重要作用。在海区水华爆发期间,可以尝试建立该函数关系来预测TEP含量,为水华监测预警提供理论基础。

    TEP对碳循环的重要性有两方面:一是TEP本身直接影响碳通量,二是TEP通过聚集作用影响非TEP颗粒的沉降[3-4]。本研究发现两种硅藻的TEP是富含碳的,其 C∶N比范围为8.400±1.39(mol∶mol)~12.98±2.80(mol∶mol),高于Redfield比值(C∶N=106∶16),与Mari等[22]对中肋骨条藻、威氏海链藻TEP C∶N比值结果相似。Engel等[3]则研究发现4种硅藻的TEP C∶N甚至能高达Redfield比值的4倍。说明TEP本身的含碳量普遍高于其他海洋生物有机颗粒,能直接对海洋碳通量做出贡献。Thornton等人[9]研究显示,在发生水华时,高浓度TEP会凝聚大量浮游植物、碎屑、小型浮游动物等非TEP颗粒物,随后发生沉降,导致水华终止。在Santa Barbaba海峡,由TEP沉降而输出的碳占总有机颗粒碳输出量的30%[23]。TEP的高黏附特性及其高碳氮比特点促使其在沉降过程中能将更多的碳沉降至深海,或长期封存在海底。因此,TEP的形成和沉降可作为一种反馈机制,将丰富的碳沉降至深海的同时,海洋浮游植物需从大气吸收更多的CO2来维持海表层平衡,这可能对全球变暖起到调节反馈作用。

3.   结论
  • (1)两种硅藻产生TEP会随生长时期和物种种类的不同而不同,具有种间差异性。两种硅藻产生TEP的来源方式可能不同。窄隙角毛藻比布氏双尾藻产TEP的效率更高。

    (2)在指数期,两种硅藻的TEP与Chl a之间均存在函数关系:TEP=α(Chl aβ,说明水华爆发期间,可以尝试运用该函数关系来预测TEP含量。

    (3)两种硅藻TEP 的C∶N范围为8.40±1.39(mol:mol)~12.98±2.80(mol:mol),高于Redfield比值(C∶N=106∶16),说明TEP富含高碳量,能对海洋碳循环做出直接贡献。

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