印太交汇区微微型浮游植物在硅循环中的贡献

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	印太交汇区微微型浮游植物在硅循环中的贡献
	王凤
学位类型	博士
导师	孙晓霞
	2024-05-15
学位授予单位	中国科学院大学
学位授予地点	中国科学院海洋研究所
关键词	印太交汇区微微型浮游植物生物硅生产速率海洋硅循环
摘要	硅是海洋中硅藻体生产所需的基本元素，理解硅循环对于认识海洋食物网、生物地球化学循环和生物碳泵的功能至关重要。先前在研究硅循环的生物组成部分时，并没有将微微型浮游植物纳入其中。而对微微型浮游植物的研究大多是关于其生态型和全球分布，对其在硅循环中的重要贡献知之甚少。尤其在全球气候变化愈演愈烈的背景下，寡营养环流面积的扩张，以及开放海洋中硅藻生物量的下降，更凸显出了解海洋微微型浮游植物对海洋硅循环的重要性。本研究率先在微微型浮游植物占主导的印太交汇区（包括东印度洋、南海、西太平洋）开展调查，旨在通过定性和定量的评估，深入探究微微型浮游植物对海洋硅循环的贡献。首先分析了印太交汇区微微型浮游植物群落结构的空间分布格局，结合水文特征阐述了环境因素对群落结构的驱动作用。在此基础上，进一步讨论了调查海域内生物硅（bSi）总储量和生产速率的分布特征和动态变化，以及微微型浮游植物在 bSi 生产活动中发挥的作用。然后结合不同海区的环境特征（温度、盐度、营养盐等），对小粒径 bSi（bSi<2 μm）和 bSi 总储量（bSiTotal），及其生产速率（ρbSi）进行相关性分析，讨论调控其空间变化潜在的影响因素。最后对微微型浮游植物—聚球藻单个细胞内的硅含量开展高精度测量，探究了不同海域中单个聚球藻细胞内硅含量的变化情况。主要研究结果和结论如下：（1）原绿球藻是寡营养海洋中生物量的主要贡献者。在印太交汇区，原绿球藻细胞是最丰富的（平均最高细胞丰度为 1.3±0.9×105 cells mL-1，西太平洋），其优势显著高于聚球藻和微微型真核藻类，并且在印太交汇区中的平均丰度占比约为 80%，尤其是在西太平洋中的占比最高。聚球藻和微微型真核藻类在群落中的占比分别在 10~20%，1~3%左右。从微微型浮游植物的地理分布来看，原绿球藻更适宜温暖的寡营养区域，密集的分布在温暖的开阔大洋中。聚球藻则在近岸表现出较高的细胞丰度，微微型真核藻类具有与聚球藻相似的分布模式，但由于其丰度值较低，因此空间差异性不明显。三种藻类在真光层水柱中的垂直分布趋势有一个共性，都集中分布在 75 m 以浅的水层中，当水深超过 100 m 后，三种藻类的丰度显著下降。通过相关性分析，发现微微型浮游植物空间分布的变异性与环境因素密切相关，这意味着印太交汇区的环境差异在很大程度上影响着浮游植物的分布情况。此外，环境因子对微微型浮游植物的影响效应在不同水层中具有不同的结果，并且温度和营养盐（特别是 DIN）被证明是调控微微型浮游植物群落动态变化较为重要的环境因子。（2）在调查区域中，我们发现 bSi<2 μm对 bSiTotal的贡献持续稳定存在，这说明微微型浮游植物在海洋 bSi 现存量中具有不可忽视的贡献。具体来看，bSi<2 μm 和 bSiTotal在南海区域的平均浓度最高，分别为 82.0±68.1 nmol Si L-1，414.2±488.8nmol Si L-1，但是 bSi<2 μm在 bSiTotal中所占的百分比在东印度洋最高，接近 30%。此外，我们没有观察到不同水层中 bSi<2 μm和 bSiTotal存在显著差异的情况，这表明 bSi 现存量在水柱中保持着稳定的分布。在 bSi 现存量最高的海区—南海中，我们发现 bSi<2 μm受环境变化的影响不显著，但是 bSiTotal与营养盐（DIP，DSi）之间存在显著的负相关性。另一方面，聚球藻与 bSi<2 μm和 bSiTotal之间都具有正相关性。（3）进一步对微微型浮游植物参与 bSi 生产活动分析发现，在东印度洋和西太平洋，微微型浮游植物的 bSi 生产速率在总生产速率中所占的比例超过了50%，明显高于其在总储量中的贡献，表明微微型浮游植物在 bSi 生产活动中发挥的重要作用可能超过硅藻。其中，ρbSi<2 μm在南海和西太平洋的表层中平均速率最高（分别是 130.5±50.9 nmol Si L-1 d-1，134.7±31.7 nmol Si L-1 d-1），ρTotal 在南海的表层中平均速率最高（303.6±137.1 nmol Si L -1 d-1），但是研究发现 bSi生产速率的波动性较大，同一海域生产速率相差十多倍。ρbSi<2 μm 对ρTotal 的占比在 75 m 水层中高于表层中的比例，表明微微型浮游植物的 bSi 生产活动在 75 m水层中更为活跃。在生产速率较高的南海中，通过相关性分析我们发现，表层和75 m 水层生产速率的影响因素不同，表层生产速率与所有的因素之间无显著相关性，而在 75 m 水层中，盐度和营养盐对生产速率起到了负相关性，聚球藻则显示出显著的正相关性。（4）聚球藻细胞内普遍存在硅累积作用，这部分硅含量也占据了一定的比例。研究发现单细胞聚球藻中的硅配额大小不受其细胞丰度和环境中硅酸盐浓度的影响，但是不同细胞内硅配额的差异较大。其中，聚球藻细胞内的硅配额在南海的浓度较高，最高浓度约为 576.4 amol Si cell-1，平均浓度为 67.4±59.8 amol Sicell-1，约是东印度洋和西太平洋平均浓度的三倍。所以，作为 bSi 生产活动的主要参与者之一，聚球藻在海洋中的分布和生物量会直接作用于 bSi 的累积速率和分布格局，进而影响海洋硅循环的稳定性。此外，细胞硅配额的变化对生物碳泵有重要影响。由于SiO2是致密的，每个细胞中 SiO2含量的增加可能会增加颗粒下沉速率，并增强碳向深海的运输。另一方面，从系统发育的角度来看，原绿球藻与聚球藻之间存在很大的相似性。基于这种相似性，我们假设原绿球藻细胞内也存在硅累积现象，这意味着微微型浮游植物可能对海洋硅循环产生着重大影响。研究结果表明，这些微微型浮游植物在印太交汇区 bSi 的生产过程中发挥着关键作用，是生物泵的关键组成部分，在很大程度上控制着碳从表层向深海的运输。如果这一观察结果在全球范围内得到验证，将会极大地改变人们对贫营养海洋中 bSi 动态的理解，并使过去将 bSi 通量视为硅藻输出的特定度量标准的解释得以重新审视。这项研究为我们提供了更深入地认识含硅微小浮游植物在全球意义上的重要性的机会，并最终将这一组成部分纳入生物地球化学模型中，以更全面地理解海洋硅循环的复杂性
其他摘要	Silicon (Si) is an essential element required for the production of diatom frustules in the marine environment, understanding the Si cycle is critical for understanding the functioning of marine food webs, biogeochemical cycles, and the biological carbon pump. Previous studies of the biological components of the Si cycle did not include the part of picoplankton. Indeed, most of the research on picoplankton has focused on their ecotypes and global distribution, and little is known about their important contribution to the Si cycle. Particularly in the context of worsening global climate change, the expansion of oligotrophic regions, and the decline of diatom biomass in open oceans over a decade, highlighting the importance of understanding the role of picoplankton in the Si cycle. This study is the first to investigate the Indo-Pacific convergence region (including the Eastern Indian Ocean, EIO; the South China Sea, SCS; and the Western Pacific Ocean, WPO) dominated by picoplankton, aiming to deeply investigate the contribution of picoplankton to the marine Si cycle through qualitative and quantitative assessment. We first analyzed the spatial distribution pattern of the picoplankton community structure in the Indo-Pacific convergence region, and stated the driving effect of environmental factors on the community structure in conjunction with the hydrographic characteristics. And then, we further discussed the distribution characteristics and dynamic changes of size-fractionated bSi reserves and production rates in the surveyed sea area, and the role of picoplankton in bSi production activities. Combined the environmental characteristics of different sea areas (temperature, salinity, nutrients, etc.), we analyze the relationships between bSi_<2_μm and bSi_Total, as well as their production rates with environmental factors, and discussed the potential influencing factors regulating their spatial variations. Finally, we carried out high-precision measurements of silicon content in individual Synechococcus cells to investigate the variation of silicon content in Synechococcus cells in different sea areas. The main findings are as follows: Prochlorococcus is a major contributor to biomass in oligotrophic oceans. Certainly, Prochlorococcus was the most abundant picoplankton in the Indo-Pacific convergence region (averaging 1.3±0.9×10⁵ cells mL^-1, in the WPO), with a significant predominance over the Synechococcus and picoeukaryotes, The average abundance of Prochlorococcus in the Indo-Pacific convergence region is about 80%, especially the highest abundance is in the WPO. The abundance of Synechococcus and picoeukaryotes in the community ranged from 10 to 20% and 1 to 3%, respectively. From the geographical distribution of picoplankton, we found that Prochlorococcus favored warm oligotrophic regions, and was densely distributed in the warm open ocean. While Synechococcus showed a high cellular abundance in the nearshore, picoeukaryotes had a similar distribution pattern to Synechococcus, but the spatial variability was not obvious due to their lower abundance. The vertical distribution of the three groups in the water column has a common feature, which is concentrated in the shallow water layer of 75 m. When the water depth exceeds 100 m, the abundance of these groups decreases significantly. Through correlation analysis, it was found that the spatial distribution variability of picoplankton was closely related to environmental factors, which means that the environmental differences in different regions greatly affected the distribution of picoplankton. In addition, the effects of environmental factors on picoplankton have different results in different water layers, temperature and nutrients (especially DIN) have been proved to be the more important environmental factors regulating the dynamics of picoplankton communities. In our investigated area, we found that the contribution of bSi_{<2 μm} to bSi_Total persisted and stabilized, suggesting that picoplankton have a non-negligible contribution to the bSi standing stock. Specifically, bSi_{<2 μm} and bSi_Total had the highest average concentrations in the SCS, were 82.0±68.1 nmol Si L^-1 and 414.2±488.8 nmol Si L^-1, respectively. but the percentage of bSi_{<2 μm} in bSi_Total was the highest in the EIO, nearly 30%. In addition, we did not observe significant differences between bSi_{<2 μm} and bSi_Total in the water column, suggesting that bSi standing stock maintains a stable distribution in the euoptical layer. In the SCS, where with the highest bSi standing stock, we found that bSi_{<2 μm} was not significantly affected by environmental changes, but there was a significant negative correlation between bSi_Total and nutrients (DIP, DSi). On the other hand, there was a positive correlation between Synechococcus and both bSi_{<2 μm} and bSi_Total. Furthermore, we conducted a detailed analysis of the involvement of picoplankton in bSi production activities, and found that in the EIO and WPO, the bSi production rate of picoplankton accounted for more than 50% of the total production rate, which was significantly higher than their contribution to the bSi standing stock, indicating that picoplankton may play an important role in bSi production activities than diatoms. Among them, ρ_{bSi<2 μm} had the highest average rate in the surface layer of the SCS and the WPO (130.5±50.9 nmol Si L^-1 d^-1 and 134.7±31.7 nmol Si L^-1 d^-1, respectively), and ρ_Total had the highest average rate in the surface layer of the SCS (303.6±137.1 nmol Si L^-1 d^-1), but it was found that the production rate of bSi fluctuates greatly, with a more than 10-fold difference in the same area. ρ_{bSi<2 μm} to ρ_Total was higher in the 75 m layer than in the surface layer, indicating that the bSi production activity of picoplankton was more active in the 75 m layer. In the SCS, where production rates were higher, the correlation analysis shows that the factors affecting production rates were different in the surface and 75 m water layers, with no significant correlation between production rates and all factors in the surface layer, whereas salinity and nutrients played a negative correlation on production rates in the 75 m water layer, and Synechococcus showed a significant positive correlation. Silicon accumulation is prevalent within the cells of Synechococcus, and this fraction also accounts for a certain percentage. We found that the single-cell Si quotas of field-collected Synechococcus was not affected by its cellular abundance or environmental Si(OH)₄ concentration, but the Si quota varied considerably within different cells. Besides, Synechococcus cellular Si quotas was higher in the SCS, with the highest concentration of 576.4 amol Si cell^-1, and an average of 67.4±59.8 amol Si cell^-1, which was about three times the average concentration in the EIO and WPO. Therefore, as one of the major participants in bSi production activities, the distribution and biomass of Synechococcus in the ocean will directly affect the accumulation rate and distribution pattern of bSi, and then influence the stability of the marine Si cycle. Besides, changes in cellular Si quota have significant consequences for the biological C pump. Because SiO₂ is dense, an increase in the amount of SiO₂ per cell may increase particle sinking rate and enhance carbon transport to the deep ocean. On the other hand, there is a great phylogenetic similarity between Prochlorococcus and Synechococcus. So we hypothesize that Si accumulation also exists in the Prochlorococcus cells, this implies that picoplankton may have a significant impact on the marine Si cycle. Our results show that picoplankton plays a key role in the bSi standing stock and production, and is a crucial component of the biological pump, and largely governs carbon transport from the surface to the deep ocean. If valid globally, this observation might substantially change understanding of silica dynamics in the oligotrophic oceans and previous interpretations of bSi fluxes as a specific metric for diatom export. This research contributes to a better understanding of the global significance of siliceous picoplankton and ultimately include this component of the marine silica cycle into biogeochemical models.
语种	中文
目录	第1章绪论 1.1 海洋浮游植物概述 1.2 海洋中的硅循环 1.2.1 硅藻在硅循环中的作用 1.2.2 微微型浮游植物在硅循环中的作用 1.3 印太交汇区环境概述 1.3.1 印度洋 1.3.2 南海 1.3.3 太平洋 1.4 研究目标和拟解决关键问题第2章材料与方法 2.1 调查站位设置 2.1.1 东印度洋调查站位 2.1.2 南海中部调查站位 2.1.3 西太平洋调查站位 2.2 采样及分析方法 2.2.1 叶绿素 2.2.2 营养盐 2.2.3 微微型浮游植物细胞丰度 2.2.4 生物硅现存量 2.2.5 生物硅生产速率 2.2.6 聚球藻细胞内硅含量 2.3 数据统计第3章微微型浮游植物在东印度洋硅循环中的贡献 3.1 结果 3.1.1 水文生化参数 3.1.2 微微型浮游植物群落组分及相关性分析 3.1.3 生物硅现存量及相关性分析 3.1.4 生物硅生产速率及相关性分析 3.1.5 聚球藻生物硅现存量 3.2 讨论 3.2.1 微微型浮游植物群落动态变化的调控因素 3.2.2 生物硅现存量及生产速率动态变化的调控因素 3.2.3 海洋聚球藻细胞对生物硅的潜在贡献 3.3 小结第4章微微型浮游植物在南海硅循环中的贡献 4.1 结果 4.1.1 水文生化参数 4.1.2 微微型浮游植物群落组分及相关性分析 4.1.3 生物硅现存量及相关性分析 4.1.4 生物硅生产速率及相关性分析 4.1.5 聚球藻细胞内硅含量 4.2 讨论 4.2.1 微微型浮游植物群落动态变化的调控因素 4.2.2 生物硅现存量及生产速率动态变化的调控因素 4.2.3 海洋聚球藻细胞对生物硅的潜在贡献 4.3 小结第5章微微型浮游植物在西太平洋硅循环中的贡献 5.1 结果 5.1.1 水文生化参数 5.1.2 微微型浮游植物群落组分及相关性分析 5.1.3 生物硅现存量及相关性分析 5.1.4 生物硅生产速率及相关性分析 5.1.5 聚球藻细胞内硅含量 5.2 讨论 5.2.1 微微型浮游植物群落动态变化的调控因素 5.2.2 生物硅现存量及生产速率动态变化的调控因素 5.2.3 海洋聚球藻细胞对生物硅的潜在贡献 5.3 小结第6章印太交汇区微微型浮游植物生物硅生产活动的对比研究 6.1 结果 6.1.1 印太交汇区微微型浮游植物群落组分的对比研究 6.1.2 印太交汇区生物硅现存量的对比研究 6.1.3 印太交汇区生物硅生产速率的对比研究 6.1.4 印太交汇区聚球藻细胞硅含量的对比研究 6.2 讨论 6.2.1 微微型浮游植物群落动态变化的调控因素 6.2.2 生物硅现存量及生产速率动态变化的调控因素 6.2.3 海洋聚球藻细胞对生物硅的潜在贡献 6.3 小结第7章结论与展望 7.1 主要研究结论 7.2 本研究创新点 7.3 展望参考文献致谢 99 作者简历及攻读学位期间发表的学术论文与其他相关学术成果 101
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/185185
专题	中国科学院海洋研究所胶州湾海洋生态系统国家野外研究站
推荐引用方式 GB/T 7714	王凤. 印太交汇区微微型浮游植物在硅循环中的贡献[D]. 中国科学院海洋研究所. 中国科学院大学,2024.

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