中国科学院海洋研究所机构知识库

       作为海洋中有机碳库和有机氮库的重要组成，氨基酸可有效指示海洋有机质的降解程度和成岩状态，进而对于科学评估有机质在海洋中的迁移转化过程与埋藏具有重要意义。本学位论文基于胶州湾颗粒物与表层沉积物中氨基酸的含量、组成、构型和分布特征的系统研究，根据氨基酸的碳氮归一化产率、降解因子、反应活性指数、D型氨基酸占比及非蛋白质氨基酸占比等降解指示因子结合碳氮比和碳稳定同位素解析了胶州湾颗粒物和沉积物中有机质的来源与降解程度，并利用细菌贡献率、细菌丰度、群落结构以及胞外肽酶活性等参数探析了微生物在海洋有机质迁移转化过程中的降解作用和有机质贡献，获得了如下主要研究结论：
1. 基于氨基酸含量及组成的降解指示因子一致指示了胶州湾颗粒有机质的降解程度，2016年秋季胶州湾颗粒态有机质的降解程度均呈现湾外高于湾内、湾内东部高于西部的变化趋势，而2017年春季则表现为湾内西部和湾外东部颗粒有机质降解程度较高的特征。颗粒有机质的来源是控制其降解程度的关键因素，海源自生有机质的贡献较多导致颗粒有机质相对新鲜，促进了细菌的大量繁殖而产生较高的细菌有机质贡献率，而陆源有机质贡献较多会导致有机质降解程度较高，更有利于诱导细菌产生较高活性的胞外肽酶来分解有机质。此外，颗粒物中细菌群落结构的变化同样改变着有机质的含量与组成，γ-变形杆菌在颗粒有机质的降解过程中起到重要作用。
       2016年秋季胶州湾海水中颗粒态氨基酸含量为1.15 ± 0.87μmol/L，由于湾内较高浮游植物丰度与湾内东部较高的陆源有机质输入的共同影响，胶州湾表层水体中颗粒态氨基酸呈现湾内高于湾外、湾内西部高于东部的趋势。有机质降解程度的指示因子，如碳氮归一化产率、降解因子DI、反应活性指数RI以及D型氨基酸占比都保持较高的一致性，表现为胶州湾湾外颗粒物中有机质降解程度高于湾内的特征，且由于湾内东部陆源有机质输入较高，导致湾内中部和东北部降解程度较高。D-AA含量、异养细菌丰度以及细菌有机质对有机碳和有机氮的贡献率均体现了细菌与有机质降解密切相关且细菌有机质对胶州湾颗粒有机质具有较为重要的贡献作用。新鲜有机质可以促进细菌的生长与繁殖，从而促进细菌对有机质的降解与转化。此外，有机质的生物活性可以影响细菌的胞外肽酶活性，湾内东北部难降解有机质可诱导细菌释放更高活性的胞外酶。胶州湾颗粒物中细菌优势类群为γ-变形菌、α-变形菌、蓝细菌门和拟杆菌门。其中蓝细菌为光合自养细菌，其相对丰度的升高可导致D-AA的相对降低，此外γ-变形菌与有机质关系密切，其相互影响机制需进一步研究。
       2017年春季胶州湾海水中颗粒氨基酸含量为0.98 ± 0.32 μmol/L，相比较低于2016年秋季。在表层水体中，颗粒态氨基酸在湾内东部海域具有较高含量且有机质较为新鲜，湾内西部海域具有较低含量的氨基酸但有机质的降解程度相对较高，湾外靠湾口海域颗粒态氨基酸含量较低但有机质较为新鲜，与湾内西部相似湾外最东部海域氨基酸含量较低且有机质降解程度较高。2017年春季胶州湾颗粒物中细菌有机质对有机碳的贡献率为17.51% ± 8.09%，对有机氮的贡献率为10.25% ± 5.96%，分布趋势呈现为湾外高于湾内，且湾内东部高于湾内西部的整体趋势。与2016年秋季相同，2017年春季胶州湾颗粒物中细菌群落的优势种为变形菌、拟杆菌和蓝细菌，但其中蓝细菌占比明显降低，仅占2016年秋季比例的一半左右。通过群落结构以及与有机质含量对比分析发现，γ-变形杆菌对POC具有重要的降解作用，其优势度越高越不利于颗粒有机碳的保存。由于光合自养细菌有机质不含有D-Asx和D-Ser，因此蓝细菌的占比对D型氨基酸的比例具有一定程度地影响作用。
2. 2016年秋季胶州湾表层沉积物中有机质的降解程度与颗粒物一致，同样表现为湾外高于湾内、湾内东部高于西部的变化趋势，有机质来源、微生物活性与上覆水水深共同影响了有机质的降解程度。湾内西部海源新鲜有机质输入较多，有利于细菌有机质的合成从而产生较高的细菌贡献率，而湾内东部较高的陆源有机质贡献决定了较高的降解程度和胞外肽酶活性。湾外较深的水深使颗粒物在沉降至沉积物之前受到更深程度的降解，致使沉积物中有机质降解程度相对高于颗粒物。
       2016年秋季胶州湾表层沉积物中总可水解氨基酸的含量为7.60 ± 3.64 μmol/g，其水平分布呈现湾内高于湾外、湾内东部高于西部的趋势。湾内西部海源新鲜有机质的输入以及较高的微生物活性、东部较高的陆源有机质输入比例、湾外水深较深均影响着沉积物中有机质降解程度。指示有机质降解程度的多项参数（THAA-C%、THAA-N%、DI、RI以及mol% D-AA）均指示沉积物中有机质降解程度表现为湾外高于湾内，湾内西部低于东部的趋势。同时沉积物中有机质的降解程度相对高于颗粒有机质，指示了沉积物中有机质经过了细菌更深程度的降解。胶州湾沉积物中对有机碳的细菌源贡献率（31.51% ± 19.17%）呈现湾内西部和湾外高于湾内东部的特征。此外，胞外肽酶活性与有机质的降解程度密切相关，不同来源的有机质具有不同的反应活性，从而产生不同的细菌源有机质的贡献率及胞外肽酶活性，沉积物中有机质越新鲜细菌贡献率越高但会抑制胞外酶的活性。细菌参与沉积物中有机质的生物降解过程，其产生的D型氨基酸对降解程度具有重要指示作用，并且细菌源有机质对沉积物有机质具有重要贡献，因此细菌是沉积物中有机质在迁移转化过程重要的调控因素。沉积物与颗粒物中氨基酸的含量和有机质降解指示因子的对比表明沉积物中有机质经过微生物更深程度的降解与利用，因此沉积物中有机质相对具有更高降解程度，且不同于颗粒物，沉积物中γ-变形菌和δ-变形菌为优势类群。
 

       As an important component of marine organic carbon pools and organic nitrogen pools, amino acids can effectively indicate the degradation states and diagenetic conditions of marine organic matter, and thus have important implications for the scientific evaluation of organic matter migration, transformation, and burial in the ocean. Firstly, the content, composition, configuration, and distribution characteristics of amino acids in particulate matters and surface sediments of Jiaozhou Bay were studied. Combined with carbon-nitrogen ratio and carbon stable isotopes, the degradation indicators, such as carbon and nitrogen normalized yield of amino acid, degradation index, reactivity index, the mole percent of D-amino acid, and mole percent of non-protein amino acid, were used to analyzed the source and degradation degree of organic matter in particulates and sediments of Jiaozhou Bay. Meanwhile, bacterial contributions, bacterial abundance, community structure of bacteria, and extracellular enzyme activity of peptidase were used to analyze the bacterial degradation and bacterial contribution to marine organic matters. The main results are as follows:
1. The degradation indicators based on amino acid content and composition all congruously indicated the degradation statues of organic matters in Jiaozhou Bay. In autumn, the degradation degree of particulate organic matter in Jiaozhou Bay showed that the degradation states in the outer bay were higher than those in the inner bay and the degradation states in the eastern inner bay were higher than those in the western inner bay. While in spring, it was characterized by higher degree of organic matter degradation in the western inner bay and the eastern outer bay. The sources of particulate organic matters were the key factors controlling the organic matter degradation states. The contribution of marine organic matter caused fresher particulate organic matter, at the same time, it promoted the proliferation of bacteria and results in a higher bacterial contribution to organic matter. While the higher contribution of terrestrial organic matter led to a higher degradation degree of organic matters, and conduce to a higher activity of extracellular peptidases to decompose organic matter producing by bacteria. In addition, the changes in bacterial community structure in the particles also change the content and composition of organic matter, Gammaproteobacteria played an important role in the degradation of organic matter.
       The content of particulate amino acids in seawater of bacteria in autumn was 1.15 ± 0.87μmol/L. Due to the combined effect of the higher phytoplankton abundance in the inner bay and the higher input of terrigenous organic matter in the eastern inner bay, the concentrations of particulate amino acids showed the tendency of higher values in the surface water of inner bay of Jiaozhou Bay, and the contents in the western area was higher than the western inner bay. The indicators of organic matter degradation, such as carbon and nitrogen normalized yield, degradation index (DI), reactivity index (RI), and mol% D-amino acid all had the similar trend, indicating that the degradation statue in the outer bay was higher than the inner bay, and the particulate organic matters central and northeastern area had the higher degradation states because of higher terrigenous organic matter input. The distributions of concentration of D-AA, bacterial abundance, and bacterial contribution to organic carbon and organic nitrogen all reflected that bacteria were closely related to the organic matter degradation, and bacterial played an important role in the particulate organic matter of Jiaozhou Bay. Fresh organic matter can promote the growth and reproduction of bacteria, thereby promoting the degradation and transformation of organic matter by bacteria. In addition, the biological activity of organic matter can affect the activity of extracellular peptidase from bacteria, and old organic matter can induce the release of extracellular peptidase having high activity. The dominant taxa in Jiaozhou Bay were Alphaproteobacteria, Gammaproteobacteria, Cyanobacteria, and Bacteroidetes. Cyanobacteria are photosynthetic and autotrophic bacteria, and their higher relative proportion can lead to a relative decrease in D-AA. Furthermore, the Gammaproteobacteria had a close relationship with organic matter, and their influence mechanism needs further study.
       The particulate amino acids contents of Jiaozhou Bay in spring was 0.98 ± 0.32 μmol/L, which was lower than in autumn. In the surface water, the particulate amino acids had higher contents in the eastern inner bay where organic matter was relatively fresher. The western inner bay had lower concentrations of amino acids, but the degradation states of particulate organic matter were higher, and the contents of particulate amino acids in the western outer bay were lower but fresher, and the amino acids had lower contents and were older in the eastern outer bay. The bacterial contribution to the particulate organic carbon in Jiaozhou Bay in spring was 17.51% ± 8.09%, and 10.25% ± 5.96% to organic nitrogen. The tendency showed the higher value in the outer bay than the inner bay, in which eastern inner bay had higher values. Like autumn, the dominant taxa of bacterial in spring were Proteobacteria, Cyanobacteria, and Bacteroidetes, but the proportion of Cyanobacteria decreased significantly in spring, only accounting for about half of the proportion in autumn. Through the comparison of community structure and concentration of organic matter, it was found that Gammaproteobacteria played an important role in the degradation of particulate organic matter, the high dominance of that taxon was not conducive to the preservation of particulate organic matter. Because photosynthetic autotrophic bacteria organic matter does not contain D-Asx and D-Ser, the proportion of Cyanobacteria has a certain influence on the proportion of D-amino acids.
2. The degradation states of organic matter in the surface sediments were consistent with those of particulate matter of Jiaozhou Bay in the autumn, it also showed that the degradation states of organic matter in the outer bay were higher than those in the inner bay, and the degradation states in the eastern inner bay were higher than those in the western inner bay. The sources of organic matter, microbial activity and depth of overlying water affected the degradation of organic matter. The input of fresh organic matter in the western inner bay was more conducive to the synthesis of bacterial organic matter, which results in higher bacterial contributions to organic matter. The contribution of higher terrestrial organic matter in the eastern inner bay determines the higher degradation states of organic matter and extracellular enzyme activity of peptidase. The deeper water depth in the outer bay caused deeper degradation of the particulate matters before it settled into the sediments, resulting in relatively higher degradation statues of organic matters in the sediments than particulate matters.
       The contents of total hydrolyzable amino acids in the surface sediments of Jiaozhou Bay was 7.60 ± 3.64 μmol/g. The horizontal distribution showed that the concentrations were higher in the outer bay than the inner bay, and the concentrations the eastern inner bay were higher than the western inner bay. The input of fresh organic matter, high microbial activity, and high contribution of terrestrial organic matter in the eastern inner bay, and deep depth of water in the outer bay were all important factors resulting in the diversity of degradation states in sediments of Jiaozhou Bay. The indicators of degradation states of organic matter reflected the degradation degrees showed that the organic matters were older in the outer bay, and in the western inner bay organic matters were fresher than the eastern inner bay. Besides, the degradation degrees in sediments were higher than particulate matters, indicating that the organic matter in the sediments had deeper degradation by microorganisms.
       The bacterial contributions in the sediments of Jiaozhou Bay presented that the contributions were higher in the western inner bay than the eastern inner bay and outer bay. In addition, the activity of extracellular peptidase was closely related to the degradation degree of organic matter in sediments. Different sources of organic matter have different reactivity, resulting in different contributions of bacterial organic matter and extracellular peptidase activity, the fresher organic matter in the sediments had the higher bacterial contribution but inhibited the expression of extracellular peptidase. Bacteria were involved in the biodegradation process of organic matter in sediments, the D-AA produced by bacteria played an important role in determining the statue of degradation, and the bacterial organic matter had important contributions to organic matter. Therefore, bacteria are the significant regulatory factors in the migration and transformation of organic matter in sediments.