杜氏盐藻藻液中溶解有机物(DOM)和透明胞外聚合物(TEP)的光化学行为研究

Photochemical Behaviour of Dissolved Organic Matter (DOM) and Transparent Exopolymer Particles (TEP) in the Algal Sap of Dunaliella salina

中文关键词: 透明胞外聚合颗粒物(TEP)  溶解性有机物(DOM)  杜氏盐藻  光化学反应  

英文关键词: Transparent Exopolymer Particles (TEP)  Dissolved Organic Matter (DOM)  Dunaliella salina  Photochemical Reactions  

中文摘要:

      杜氏盐藻(Dunaliella salina)是一种适应于高盐海水环境的微藻，作为海洋生态系统中的初级生产者，能够通过光合作用合成并分泌大量的溶解性有机物(Dissolved Organic Matter, DOM)以及透明胞外聚合物(Transparent Exopolymer Particles, TEP)，这些分泌物是海洋中自生源大分子物质的重要来源，对海洋生物地球化学循环具有显著的影响。本文选取杜氏盐藻为研究对象，探究光照条件下杜氏盐藻介导有色溶解有机物(Colored Dissolved Organic Matter, CDOM)、碳水化合物(多糖和单糖)和TEP的组分变化以及这些有机物之间的相互关系。结果表明，无藻环境中的CDOM发生光降解，导致大分子化合物裂解 形成小分子化合物或分解为无机物，其生成单糖量较大；而在有藻环境中，由于藻类的影响，光化学反应促进了DOM的生成，且多糖的生成量增加；通过三维荧光光谱-平行因子分析(EEMs-PARAFAC)模型，分析荧光溶解性有机质（FDOM），共鉴定出5种荧光组分，3种类蛋白质组分（C1、C2和C3）和2种腐殖质样组分（C4和C5），无论在有藻还是无藻环境中，均以类色氨酸基团为主，DOM多来源于藻光合作用和死亡分解的产物。本研究还发现尽管光降解是TEP损失的重要过程，但仍存在DOM发生光聚合自发凝聚形成TEP的过程，藻类以及微生物也会释放新的TEP，但其释放的量以及光聚合的量均小于光降解的量；此外，相关性研究发现无藻环境中碳水化合物（多糖和单糖）与TEP之间均无显著相关性，但微藻环境下多糖(R2=0.822，p＜0.05)和单糖(R2=0.821，p＜0.05)与TEP浓度之间呈现显著负相关；而CDOM与TEP在无藻环境中表现为正相关(R2=0.698，p＜0.05)，有藻环境表现为较弱的负相关(R2=0.612，p=0.07)，这表明微藻显著影响了CDOM、碳水化合物(多糖和单糖)与TEP之间的光化学转化过程。本研究为解释在微藻环境下DOM、碳水化合物和TEP的光反应响应机制，理解光化学过程在物质循环中的作用提供了宝贵的数据，这对于揭示海洋生物地球化学循环的复杂机制的维持具有重大的科学意义。

英文摘要:

      Dunaliella salina is a microalgae adapted to high salinity seawater environment. As a major primary producer in the ocean, it produces and releases a large amount of marine autochthonous Dissolved Organic Matter (DOM) into the environment through photosynthesis, which can be formed into Transparent Exopolymer Particles (TEPs) under suitable conditions (e.g., pH and ionic strength) through Under appropriate conditions (e.g. pH and ionic strength), they can form Transparent Exopolymer Particles (TEP) through polymerization. In addition, algal cells and bacteria also release large amounts of dissolved polysaccharides in the water column, and polysaccharide-rich fractions are good precursors for TEP formation, and these precursors can form a large number of TEPs through the process of coagulation, gelation, and annealing. In addition, TEPs can be generated through abiotic processes, and TEPs are formed by DOM at the microscale through the physical process of adsorption on surfaces and foaming. Photochemical reactions affect the formation of TEPs on the surface of the ocean. TEP formation in the surface layer, which in turn increases the transport of DOM from the sea surface to the deep sea. The photochemical process of DOM in the ocean can convert large molecules of DOM and TEP into small molecules. At the same time, gases such as carbon dioxide will be released in conversion. This process is a key factor driving the change of the oceanic DOM reservoirs and the cycling of matter, which is of great significance for the cycling of matter in seawater and deep-sea carbon sequestration. Therefore, in this study, Duchenne saline alga was selected as the research object to investigate the changes in the components of DOM, carbohydrates (polysaccharides and monosaccharides) and TEP mediated by Duchenne saline alga and the interrelationships among these organisms under the light conditions by conducting 60h light irradiation experiments on algal sap during the stable growth period. The results showed that photodegradation of CDOM in algal-free environments occurred, leading to the cleavage of macromolecular compounds to form small molecule compounds or decomposition into inorganic substances, which produced larger amounts of monosaccharides; whereas, in microalgal environments, photochemical reactions facilitated the production of DOM due to the influence of algae, and polysaccharides production was increased; through the three-dimensional fluorescence spectroscopy-parallel factor analysis (EEMs-PARAFAC) model, the analysis of fluorescent dissolved organic matter (FDOM), five fluorescent fractions, three protein-like fractions (C1, C2 and C3) and two humus-like fractions (C4 and C5) were identified, in both algal and algal-free environments, the tryptophan-like groups are predominant, and DOM is mostly derived from the products of algal photosynthesis and death decomposition. This study also found that although photodegradation is an important process of TEP loss, there still exists a process in which DOM undergoes photo-polymerization for spontaneous coalescence to form TEP, and algae as well as microorganisms also release new TEP, but the amount of their release as well as photopolymerization is smaller than the amount of photodegradation; moreover, correlation studies found that there was no significant correlation between carbohydrates (polysaccharides and monosaccharides) and TEPs in both the algal-free and microalgae environments, but the Microalgae environment showed a significant negative correlation between polysaccharides (R2=0.822, p<0.05) and monosaccharides (R2=0.821, p<0.05) and TEP concentration; while CDOM and TEP showed a positive correlation in the algal-free environment (R2=0.698, p<0.05), and a weaker negative correlation in the algal environment (R2=0.612, p=0.07),. This indicated that microalgae significantly affected the photochemical transformation process between CDOM, carbohydrates (polysaccharides and monosaccharides) and TEP. This study provides valuable data for explaining the mechanisms of DOM, carbohydrate and TEP response to light in microalgal environments, understanding the role of photochemical processes in the ocean in material cycling, including carbon and nutrient cycling, and is of great scientific significance in revealing the complex mechanisms of marine biogeochemical cycling.